diff --git a/checks.go b/checks.go
index 3510b6e..cae02f5 100644
--- a/checks.go
+++ b/checks.go
@@ -35,32 +35,32 @@ func GetHTTP(addr string, timeout time.Duration) (CheckFunc, error) {
 		timeout = DefaultTimeout
 	}
 
-	return func(ctx context.Context) (Status, error) {
+	return func(ctx context.Context) error {
 		ctx, cancel := context.WithTimeout(ctx, timeout)
 		defer cancel()
 
 		req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
 		if err != nil {
-			return StatusUnknown, fmt.Errorf("failed to create http request: %w", err)
+			return fmt.Errorf("failed to create http request: %w", err)
 		}
 
 		resp, err := http.DefaultClient.Do(req)
 		if err != nil {
-			return StatusDown, fmt.Errorf("do request failed: %w", err)
+			return fmt.Errorf("do request failed: %w", err)
 		}
 
 		defer resp.Body.Close()
 
 		body, err := io.ReadAll(resp.Body)
 		if err != nil {
-			return StatusDown, fmt.Errorf("err reading response body: %w", err)
+			return fmt.Errorf("err reading response body: %w", err)
 		}
 
 		if resp.StatusCode != http.StatusOK {
-			return StatusDown, fmt.Errorf("got HTTP response code %d, body: %s", resp.StatusCode, string(body))
+			return fmt.Errorf("got HTTP response code %d, body: %s", resp.StatusCode, string(body))
 		}
 
-		return StatusOK, nil
+		return nil
 	}, nil
 }
 
@@ -83,27 +83,27 @@ func HeadHTTP(addr string, timeout time.Duration) (CheckFunc, error) {
 		timeout = DefaultTimeout
 	}
 
-	return func(ctx context.Context) (Status, error) {
+	return func(ctx context.Context) error {
 		ctx, cancel := context.WithTimeout(ctx, timeout)
 		defer cancel()
 
 		req, err := http.NewRequestWithContext(ctx, http.MethodHead, u.String(), nil)
 		if err != nil {
-			return StatusUnknown, fmt.Errorf("failed to create http request: %w", err)
+			return fmt.Errorf("failed to create http request: %w", err)
 		}
 
 		resp, err := http.DefaultClient.Do(req)
 		if err != nil {
-			return StatusDown, fmt.Errorf("do request failed: %w", err)
+			return fmt.Errorf("do request failed: %w", err)
 		}
 
 		defer resp.Body.Close()
 
 		if resp.StatusCode != http.StatusOK {
-			return StatusDown, fmt.Errorf("got HTTP response code %d", resp.StatusCode)
+			return fmt.Errorf("got HTTP response code %d", resp.StatusCode)
 		}
 
-		return StatusOK, nil
+		return nil
 	}, nil
 }
 
@@ -121,7 +121,7 @@ func DialTCP(addr string, timeout time.Duration) (CheckFunc, error) {
 		timeout = DefaultTimeout
 	}
 
-	return func(ctx context.Context) (Status, error) {
+	return func(ctx context.Context) error {
 		deadline := time.Now().Add(timeout)
 		if t, ok := ctx.Deadline(); ok && t.Before(deadline) {
 			deadline = t
@@ -129,11 +129,11 @@ func DialTCP(addr string, timeout time.Duration) (CheckFunc, error) {
 
 		conn, err := net.DialTimeout("tcp", addr, time.Until(deadline))
 		if err != nil {
-			return StatusDown, fmt.Errorf("error dialing: %w", err)
+			return fmt.Errorf("error dialing: %w", err)
 		}
 
 		defer conn.Close()
 
-		return StatusOK, nil
+		return nil
 	}, nil
 }
diff --git a/checks_test.go b/checks_test.go
index a2417df..f113e77 100644
--- a/checks_test.go
+++ b/checks_test.go
@@ -11,6 +11,7 @@ import (
 )
 
 func TestGetHTTPSuccess(t *testing.T) {
+	t.Parallel()
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Write([]byte("OK"))
 	}))
@@ -22,30 +23,28 @@ func TestGetHTTPSuccess(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	status, err := fn(t.Context())
+	err = fn(t.Context())
 	if err != nil {
 		t.Fatal(err)
 	}
-
-	if status != watchdog.StatusOK {
-		t.Fatalf("incorrect status %s, expected %s", status, watchdog.StatusOK)
-	}
 }
 
 func TestGetHTTPError(t *testing.T) {
+	t.Parallel()
 	addr := "https://127.0.0.1:42014"
 	fn, err := watchdog.GetHTTP(addr, time.Second)
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	status, err := fn(t.Context())
-	if status != watchdog.StatusDown || err == nil {
+	err = fn(t.Context())
+	if err == nil {
 		t.Errorf("incorrect status for unavalable host")
 	}
 }
 
 func TestHeadHTTPSuccess(t *testing.T) {
+	t.Parallel()
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusOK)
 	}))
@@ -57,30 +56,28 @@ func TestHeadHTTPSuccess(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	status, err := fn(t.Context())
+	err = fn(t.Context())
 	if err != nil {
 		t.Fatal(err)
 	}
-
-	if status != watchdog.StatusOK {
-		t.Fatalf("incorrect status %s, expected %s", status, watchdog.StatusOK)
-	}
 }
 
 func TestHeadHTTPError(t *testing.T) {
+	t.Parallel()
 	addr := "https://127.0.0.1:42014"
 	fn, err := watchdog.HeadHTTP(addr, time.Second)
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	status, err := fn(t.Context())
-	if status != watchdog.StatusDown || err == nil {
+	err = fn(t.Context())
+	if err == nil {
 		t.Errorf("incorrect status for unavalable host")
 	}
 }
 
 func TestDialTCPSuccess(t *testing.T) {
+	t.Parallel()
 	addr := "127.0.0.1:42013"
 	lis, err := net.Listen("tcp", addr)
 	if err != nil {
@@ -101,18 +98,14 @@ func TestDialTCPSuccess(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	status, err := fn(t.Context())
+	err = fn(t.Context())
 	if err != nil {
 		t.Fatal(err)
 	}
-
-	if status != watchdog.StatusOK {
-		t.Error("incorrect status for available addr")
-	}
-
 }
 
 func TestDialTCPError(t *testing.T) {
+	t.Parallel()
 	addr := "127.0.0.1:65535"
 	// check for non-existent addr
 	fn, err := watchdog.DialTCP(addr, time.Second)
@@ -120,8 +113,8 @@ func TestDialTCPError(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	status, err := fn(t.Context())
-	if (status != watchdog.StatusDown) || (err == nil) {
-		t.Errorf("incorrect status %s, expected %s", status, watchdog.StatusDown)
+	err = fn(t.Context())
+	if err == nil {
+		t.Errorf("incorrect status")
 	}
 }
diff --git a/entity.go b/entity.go
index cad809f..b8f3d75 100644
--- a/entity.go
+++ b/entity.go
@@ -5,30 +5,11 @@ import (
 	"time"
 )
 
-type Status uint8
-
-const (
-	StatusUnknown Status = iota
-	StatusOK
-	StatusDown
-)
-
-func (s Status) String() string {
-	switch s {
-	case StatusOK:
-		return "OK"
-	case StatusDown:
-		return "DOWN"
-	default:
-		return "UNKNOWN"
-	}
-}
-
 // CheckFunc is a function that does the actual work.
 // This package provides a number of check functions but
 // any function matching the signature may be provided.
 // It must obey context dealine and cancellation.
-type CheckFunc func(context.Context) (Status, error)
+type CheckFunc func(context.Context) error
 
 // Check represents a check that must be run by Watchdog.
 type Check struct {
@@ -38,7 +19,6 @@ type Check struct {
 }
 
 type CheckResult struct {
-	Name   string // identifier of check
-	Status Status // status as retuned by CheckFunc
-	Error  error  // error returned by CheckFunc
+	Name  string // identifier of check
+	Error error  // error returned by CheckFunc
 }
diff --git a/go.mod b/go.mod
index bf9d428..c02d419 100644
--- a/go.mod
+++ b/go.mod
@@ -1,5 +1,5 @@
 module code.uint32.ru/tiny/watchdog
 
-go 1.24.4
+go 1.24
 
 require golang.org/x/sync v0.15.0
diff --git a/watchdog.go b/watchdog.go
index d3da178..345b6fd 100644
--- a/watchdog.go
+++ b/watchdog.go
@@ -16,17 +16,16 @@ var (
 // Watchdog keeps checks to run either periodically
 // or on demand.
 type Watchdog struct {
-	checks []*wdCheck
+	checks map[string]*wdCheck
 	mu     sync.Mutex
 
-	monitoring bool // is monitoring currently in progress
-
 	events  chan CheckResult // output channel
 	limiter chan struct{}    // TODO: use proper limiter here
 
-	timeout time.Duration
+	timeout time.Duration // timeout for checks to complete
 
-	running int
+	monitoring bool // is monitoring currently in progress
+	running    int  // number of active checks monitored
 }
 
 type wdCheck struct {
@@ -37,29 +36,26 @@ type wdCheck struct {
 // New creates instance of Watchdog with
 // provided checks.
 func New(checks ...Check) *Watchdog {
-	ch := make([]*wdCheck, len(checks))
+	w := Watchdog{
+		checks: make(map[string]*wdCheck),
+	}
 
-	for i := range checks {
-		ch[i] = &wdCheck{
-			check: checks[i],
+	for _, c := range checks {
+		nc := &wdCheck{
+			check: c,
 		}
+
+		w.checks[c.Name] = nc
 	}
 
-	w := &Watchdog{
-		checks: ch,
-	}
-
-	return w
+	return &w
 }
 
 func (w *Watchdog) ListChecks() []Check {
 	w.mu.Lock()
 	defer w.mu.Unlock()
 
-	out := make([]Check, len(w.checks))
-	for i := range w.checks {
-		out[i] = w.checks[i].check
-	}
+	out := w.copyChecks()
 
 	return out
 }
@@ -81,20 +77,31 @@ func (w *Watchdog) SetTimeout(d time.Duration) {
 // AddChecks adds checks to the group.
 // If monitoring is in progress then monitoring it started for the newly added
 // check as well.
-// Check may have duplicate Name fields but note that RemoveChecks removes checks
-// by their Name fields.
+// Check may have not have duplicate Name fields. New check with the same
+// hame overwrites the previous one.
 func (w *Watchdog) AddChecks(checks ...Check) {
 	w.mu.Lock()
 	defer w.mu.Unlock()
 
-	for i := range checks {
+	if w.checks == nil {
+		w.checks = make(map[string]*wdCheck)
+	}
+
+	for _, c := range checks {
 		nc := &wdCheck{
-			check: checks[i],
+			check: c,
 		}
-		w.checks = append(w.checks, nc)
+
+		old, haveOld := w.checks[c.Name]
+
+		w.checks[c.Name] = nc
 
 		if w.monitoring {
 			w.startMonitoring(nc)
+
+			if haveOld {
+				w.stopMonitoring(old)
+			}
 		}
 	}
 }
@@ -104,19 +111,18 @@ func (w *Watchdog) RemoveChecks(names ...string) {
 	w.mu.Lock()
 	defer w.mu.Unlock()
 
-	remaining := make([]*wdCheck, 0, len(w.checks)-len(names))
-	for _, c := range w.checks {
-		if slices.Contains(names, c.check.Name) {
-			if w.monitoring {
-				w.stopMonitoring(c)
-			}
+	for _, name := range names {
+		c, ok := w.checks[name]
+		if !ok {
 			continue
 		}
 
-		remaining = append(remaining, c)
-	}
+		if w.monitoring {
+			w.stopMonitoring(c)
+		}
 
-	w.checks = remaining
+		delete(w.checks, name)
+	}
 }
 
 // Start starts monitoring.
@@ -151,12 +157,10 @@ func (w *Watchdog) Start(concurrency int) (<-chan CheckResult, error) {
 	w.events = make(chan CheckResult, concurrency)
 	w.limiter = make(chan struct{}, concurrency)
 
-	for i := range w.checks {
-		w.startMonitoring(w.checks[i])
+	for _, c := range w.checks {
+		w.startMonitoring(c)
 	}
 
-	w.monitoring = true
-
 	return w.events, nil
 }
 
@@ -170,8 +174,8 @@ func (w *Watchdog) Stop() error {
 		return ErrNotRunning
 	}
 
-	for i := range w.checks {
-		w.stopMonitoring(w.checks[i])
+	for _, c := range w.checks {
+		w.stopMonitoring(c)
 	}
 
 	return nil
@@ -182,13 +186,14 @@ func (w *Watchdog) Stop() error {
 // Otherwise at most concurrency checks will be allowed to run simultaneously.
 func (w *Watchdog) RunImmediately(ctx context.Context, concurrency int) ([]CheckResult, error) {
 	w.mu.Lock()
+
 	if len(w.checks) == 0 {
 		w.mu.Unlock()
 		return nil, ErrNotConfigured
 	}
 
 	cp := w.copyChecks()
-	w.mu.Unlock() // release
+	w.mu.Unlock()
 
 	if concurrency == 0 {
 		concurrency = len(cp)
@@ -209,43 +214,26 @@ func (w *Watchdog) RunImmediately(ctx context.Context, concurrency int) ([]Check
 }
 
 func (w *Watchdog) copyChecks() []Check {
-	cp := make([]Check, len(w.checks))
-	for i := range w.checks {
-		cp[i] = w.checks[i].check
+	cp := make([]Check, 0, len(w.checks))
+	for _, v := range w.checks {
+		cp = append(cp, v.check)
 	}
 
 	return cp
 }
 
 func (w *Watchdog) startMonitoring(wdc *wdCheck) {
-
 	wdc.stop = make(chan struct{})
 	c := wdc.check
 
-	// this method is called only with
-	// w.mu locked
+	if !w.monitoring {
+		w.monitoring = true
+	}
+
 	w.running++
 
 	go func() {
-		defer func() {
-			w.mu.Lock()
-			defer w.mu.Unlock()
-
-			w.running--
-			if w.running == 0 {
-				// last goroutine to exit will also
-				// close the output chan
-				close(w.events)
-				w.monitoring = false
-			}
-		}()
-
-		state := CheckResult{
-			// if first run return anything
-			// other that OK, we'll report it
-			// if first run is OK, then we do not need to report
-			Status: StatusOK,
-		}
+		var curr error = nil
 
 		ticker := time.Tick(wdc.check.Interval)
 
@@ -255,21 +243,22 @@ func (w *Watchdog) startMonitoring(wdc *wdCheck) {
 			ctx, cancel := context.WithTimeout(context.Background(), w.timeout)
 			defer cancel()
 
-			status, err := c.Check(ctx)
+			err := c.Check(ctx)
 
 			<-w.limiter
 
-			s := CheckResult{
-				Name:   c.Name,
-				Status: status,
-				Error:  err,
+			r := CheckResult{
+				Name:  c.Name,
+				Error: err,
 			}
 
-			if s.Status != state.Status || s.Error != nil {
-				w.events <- s
+			if (err != nil && curr == nil) ||
+				(curr != nil && err == nil) {
+				// status changed, let's report
+				w.events <- r
 			}
 
-			state = s
+			curr = err
 
 			select {
 			case <-ticker:
@@ -284,50 +273,52 @@ func (w *Watchdog) startMonitoring(wdc *wdCheck) {
 
 func (w *Watchdog) stopMonitoring(wdc *wdCheck) {
 	close(wdc.stop)
+	w.running--
+
+	if w.running == 0 {
+		w.monitoring = false
+		close(w.events)
+	}
 }
 
 func runChecksConcurrently(ctx context.Context, ch []Check, concurrency int) []CheckResult {
-	statuses := make([]CheckResult, 0, len(ch))
-	m := sync.Mutex{} // for append operations
-
 	sema := make(chan struct{}, concurrency) // semaphore to limit concurrency
-	done := make(chan struct{}, len(ch))
-
-	count := len(ch)
+	done := make(chan CheckResult, len(ch))
 
+	wg := new(sync.WaitGroup)
+	wg.Add(len(ch))
 	for _, e := range ch {
-		sema <- struct{}{} // acquire
-		go func() error {
+		go func() {
+			sema <- struct{}{} // acquire
 			defer func() {
-				<-sema
-				done <- struct{}{}
+				<-sema // release
+				wg.Done()
 			}()
 
 			// relying on assumption that CheckFunc obeys context
 			// cancellation
-			status, err := e.Check(ctx)
+			err := e.Check(ctx)
 
 			r := CheckResult{
-				Name:   e.Name,
-				Status: status,
-				Error:  err,
+				Name:  e.Name,
+				Error: err,
 			}
 
-			m.Lock()
-			defer m.Unlock()
-			statuses = append(statuses, r)
-
-			return nil
+			done <- r
 		}()
 	}
 
-	// wait for all to finish
-	for range done {
-		count--
-		if count == 0 {
-			close(done)
-		}
+	go func() {
+		wg.Wait()
+		close(done)
+	}()
+
+	results := make([]CheckResult, 0, len(ch))
+
+	// collect results
+	for r := range done {
+		results = append(results, r)
 	}
 
-	return statuses
+	return results
 }
diff --git a/watchdog_test.go b/watchdog_test.go
index 297d9f7..ba24417 100644
--- a/watchdog_test.go
+++ b/watchdog_test.go
@@ -3,6 +3,8 @@ package watchdog_test
 import (
 	"context"
 	"errors"
+	"net/http"
+	"net/http/httptest"
 	"reflect"
 	"testing"
 	"time"
@@ -12,20 +14,19 @@ import (
 
 type mockChecker struct {
 	name   string
-	status watchdog.Status
 	err    error
 	called bool
 }
 
-func (m *mockChecker) Func(ctx context.Context) (watchdog.Status, error) {
+func (m *mockChecker) Func(ctx context.Context) error {
 	m.called = true
 
 	time.Sleep(time.Millisecond * 10)
 	if err := ctx.Err(); err != nil {
-		return watchdog.StatusUnknown, err
+		return err
 	}
 
-	return m.status, m.err
+	return m.err
 }
 
 func (m *mockChecker) HasBeenCalled() bool {
@@ -40,8 +41,8 @@ func (m *mockChecker) Check() watchdog.Check {
 	}
 }
 
-func newMockChecker(name string, s watchdog.Status, err error) *mockChecker {
-	return &mockChecker{name: name, status: s, err: err}
+func newMockChecker(name string, err error) *mockChecker {
+	return &mockChecker{name: name, err: err}
 }
 
 func TestCreateWith_new(t *testing.T) {
@@ -59,8 +60,8 @@ func TestNew(t *testing.T) {
 		t.Errorf("expected len = 0")
 	}
 
-	m1 := newMockChecker("mock", watchdog.StatusOK, nil)
-	m2 := newMockChecker("mock2", watchdog.StatusOK, nil)
+	m1 := newMockChecker("mock", nil)
+	m2 := newMockChecker("mock2", nil)
 
 	w = watchdog.New()
 	w.AddChecks(m1.Check(), m2.Check())
@@ -96,8 +97,8 @@ func TestRunImmediately(t *testing.T) {
 		t.Errorf("expected zero len slice for empty instance, got %d", len(out))
 	}
 
-	m1 := newMockChecker("mock", watchdog.StatusOK, nil)
-	m2 := newMockChecker("mock2", watchdog.StatusOK, nil)
+	m1 := newMockChecker("mock", nil)
+	m2 := newMockChecker("mock2", nil)
 
 	w = watchdog.New(m1.Check(), m2.Check())
 	out, _ = w.RunImmediately(t.Context(), 0)
@@ -119,8 +120,8 @@ func TestStartStop(t *testing.T) {
 		t.Error("Start doen't error on empty checks slice")
 	}
 
-	m1 := newMockChecker("mock", watchdog.StatusOK, nil)
-	m2 := newMockChecker("mock2", watchdog.StatusOK, nil)
+	m1 := newMockChecker("mock", nil)
+	m2 := newMockChecker("mock2", nil)
 
 	w.AddChecks(m1.Check(), m2.Check())
 
@@ -167,7 +168,7 @@ func TestStartStop(t *testing.T) {
 func TestSetTimeout(t *testing.T) {
 	w := new(watchdog.Watchdog)
 	w.SetTimeout(time.Millisecond)
-	m1 := newMockChecker("mock", watchdog.StatusOK, nil)
+	m1 := newMockChecker("mock", nil)
 	w.AddChecks(m1.Check())
 
 	out, _ := w.Start(0)
@@ -175,8 +176,67 @@ func TestSetTimeout(t *testing.T) {
 	w.Stop()
 	res := <-out
 
-	if !(res.Status == watchdog.StatusUnknown) || !errors.Is(res.Error, context.DeadlineExceeded) {
-		t.Logf("got status: %s, err: %v", res.Status, res.Error)
+	if !errors.Is(res.Error, context.DeadlineExceeded) {
+		t.Logf("got err: %v", res.Error)
 		t.Fatal("incorrect status for timed out op")
 	}
 }
+
+func TestDuplicates(t *testing.T) {
+	gethandler := func() http.HandlerFunc {
+		count := 0
+		return func(w http.ResponseWriter, r *http.Request) {
+			count++
+			if count >= 10 {
+				// we, re up again
+				w.Write([]byte("OK"))
+				return
+			}
+
+			http.Error(w, "down", http.StatusInternalServerError)
+		}
+	}
+
+	srv := httptest.NewServer(gethandler())
+
+	addr := srv.URL
+
+	fn, err := watchdog.GetHTTP(addr, time.Second)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	w := new(watchdog.Watchdog)
+
+	check := watchdog.Check{
+		Name:     "test",
+		Interval: time.Millisecond * 10,
+		Check:    fn,
+	}
+
+	w.AddChecks(check)
+	w.SetTimeout(time.Millisecond * 10)
+
+	out, err := w.Start(1000)
+	if err != nil {
+		t.Error("Start returns error", err)
+	}
+
+	go func() {
+		time.Sleep(time.Second)
+		w.Stop()
+	}()
+
+	count := 0
+
+	for range out {
+		count++
+	}
+
+	if count != 2 {
+		// must only return one event on initial failure and
+		// one event whet endpoint becomes available
+		t.Error("incorrect result count received from chan")
+		t.Log("received count is", count)
+	}
+}