diff --git a/cmd/pulse/main.go b/cmd/pulse/main.go
index 289fa4b..2baf07f 100644
--- a/cmd/pulse/main.go
+++ b/cmd/pulse/main.go
@@ -164,11 +164,29 @@ func main() {
 		}
 
 		// Check if a download client with this name already exists.
+		// If it does, update it (service may have restarted on a new port
+		// or regenerated its API key). If not, create it.
 		existing, _ := dlClientSvc.List(ctx)
 		for _, e := range existing {
 			if e.Name == svcInfo.Name {
-				logger.Info("pulse: download-client service already registered",
-					"name", svcInfo.Name, "service_id", serviceID)
+				_, updateErr := dlClientSvc.Update(ctx, e.ID, downloadclient.Input{
+					Name:     svcInfo.Name,
+					Kind:     kind,
+					Protocol: protocol,
+					Enabled:  e.Enabled,
+					Priority: int(e.Priority),
+					Host:     host,
+					Port:     port,
+					Password: svcInfo.ApiKey,
+					Settings: `{"pulse":true}`,
+				})
+				if updateErr != nil {
+					logger.Warn("pulse: failed to update download-client on re-register",
+						"name", svcInfo.Name, "error", updateErr)
+				} else {
+					logger.Info("pulse: updated download-client service on re-register",
+						"name", svcInfo.Name, "host", host, "port", port)
+				}
 				return
 			}
 		}
@@ -181,6 +199,7 @@ func main() {
 			Priority: 1,
 			Host:     host,
 			Port:     port,
+			Password: svcInfo.ApiKey,
 			Settings: `{"pulse":true}`,
 		})
 		if err != nil {
diff --git a/pkg/sdk/client.go b/pkg/sdk/client.go
index 8bfad8d..d39b5bd 100644
--- a/pkg/sdk/client.go
+++ b/pkg/sdk/client.go
@@ -59,6 +59,10 @@ type Config struct {
 	// Capabilities declares what this service supports. Optional.
 	Capabilities []string
 
+	// ServiceAPIKey is this service's own API key, shared during registration
+	// so other services that discover it via Pulse can authenticate. Optional.
+	ServiceAPIKey string
+
 	// HeartbeatInterval controls how often heartbeats are sent. Default: 30s.
 	HeartbeatInterval time.Duration
 
@@ -137,6 +141,51 @@ func New(cfg Config) (*Client, error) {
 	return c, nil
 }
 
+// NewWithRetry creates a client that retries registration with exponential
+// backoff. It tries up to 6 times over ~2 minutes (2s, 4s, 8s, 16s, 32s,
+// 32s). If Pulse is not configured (empty URL), returns nil immediately.
+// If all attempts fail, returns nil and an error — the caller should
+// continue in standalone mode.
+func NewWithRetry(cfg Config) (*Client, error) {
+	if cfg.PulseURL == "" {
+		return nil, nil
+	}
+	if cfg.Logger == nil {
+		cfg.Logger = slog.Default()
+	}
+
+	const maxAttempts = 6
+	wait := 2 * time.Second
+	maxWait := 32 * time.Second
+
+	var lastErr error
+	for attempt := 1; attempt <= maxAttempts; attempt++ {
+		c, err := New(cfg)
+		if err == nil {
+			return c, nil
+		}
+		lastErr = err
+		if attempt < maxAttempts {
+			cfg.Logger.Info("sdk: pulse unavailable, retrying",
+				"attempt", attempt,
+				"next_retry", wait,
+				"error", err,
+			)
+			time.Sleep(wait)
+			wait *= 2
+			if wait > maxWait {
+				wait = maxWait
+			}
+		}
+	}
+
+	cfg.Logger.Warn("sdk: pulse registration failed after retries, running standalone",
+		"attempts", maxAttempts,
+		"error", lastErr,
+	)
+	return nil, lastErr
+}
+
 // ServiceID returns the ID assigned by Pulse during registration.
 func (c *Client) ServiceID() string {
 	return c.serviceID
@@ -299,6 +348,9 @@ func (c *Client) register(ctx context.Context) (*Service, error) {
 		"version":      c.cfg.Version,
 		"capabilities": c.cfg.Capabilities,
 	}
+	if c.cfg.ServiceAPIKey != "" {
+		body["api_key"] = c.cfg.ServiceAPIKey
+	}
 	var svc Service
 	if err := c.doRequest(ctx, "POST", "/api/v1/services/register", body, &svc); err != nil {
 		return nil, err
@@ -308,7 +360,12 @@ func (c *Client) register(ctx context.Context) (*Service, error) {
 
 func (c *Client) heartbeatLoop(ctx context.Context) {
 	defer c.wg.Done()
-	ticker := time.NewTicker(c.cfg.HeartbeatInterval)
+
+	interval := c.cfg.HeartbeatInterval
+	maxInterval := 5 * time.Minute
+	consecutiveFailures := 0
+
+	ticker := time.NewTicker(interval)
 	defer ticker.Stop()
 
 	for {
@@ -317,7 +374,44 @@ func (c *Client) heartbeatLoop(ctx context.Context) {
 			return
 		case <-ticker.C:
 			if err := c.sendHeartbeat(ctx); err != nil {
-				c.logger.Warn("sdk: heartbeat failed", "error", err)
+				consecutiveFailures++
+				c.logger.Warn("sdk: heartbeat failed",
+					"error", err,
+					"consecutive_failures", consecutiveFailures,
+					"next_interval", interval,
+				)
+
+				// After 5 consecutive failures, try re-registering in case
+				// Pulse restarted and lost our registration.
+				if consecutiveFailures == 5 {
+					c.logger.Info("sdk: attempting re-registration after persistent heartbeat failures")
+					if svc, rerr := c.register(ctx); rerr == nil {
+						c.serviceID = svc.ID
+						c.logger.Info("sdk: re-registered with pulse", "service_id", svc.ID)
+						consecutiveFailures = 0
+						interval = c.cfg.HeartbeatInterval
+						ticker.Reset(interval)
+						continue
+					}
+				}
+
+				// Exponential backoff: 30s → 45s → 67s → ... → 5m cap
+				interval = time.Duration(float64(interval) * 1.5)
+				if interval > maxInterval {
+					interval = maxInterval
+				}
+				ticker.Reset(interval)
+			} else {
+				if consecutiveFailures > 0 {
+					c.logger.Info("sdk: heartbeat recovered",
+						"after_failures", consecutiveFailures,
+					)
+				}
+				consecutiveFailures = 0
+				if interval != c.cfg.HeartbeatInterval {
+					interval = c.cfg.HeartbeatInterval
+					ticker.Reset(interval)
+				}
 			}
 		}
 	}