diff --git a/internal/service/api/handler/devices.go b/internal/service/api/handler/devices.go
index 1e88604..389b343 100644
--- a/internal/service/api/handler/devices.go
+++ b/internal/service/api/handler/devices.go
@@ -215,6 +215,10 @@ func (h *Handler) CreateIoTDevice(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if err := h.Devices.Create(r.Context(), device); err != nil {
+		if errors.Is(err, store.ErrDeviceIDExists) {
+			writeJSON(w, http.StatusConflict, errResp("device_id already exists in this namespace"))
+			return
+		}
 		if errors.Is(err, store.ErrAlreadyExists) {
 			writeJSON(w, http.StatusConflict, errResp("iot device already exists"))
 			return
diff --git a/internal/service/store/device.go b/internal/service/store/device.go
index bfd4b34..c0c049e 100644
--- a/internal/service/store/device.go
+++ b/internal/service/store/device.go
@@ -15,6 +15,10 @@ var ErrNotFound = errors.New("device not found")
 // ErrAlreadyExists — конфликт уникальности (namespace, name) или (namespace, device_id).
 var ErrAlreadyExists = errors.New("device already exists")
 
+// ErrDeviceIDExists — конфликт именно по (namespace, device_id) (отличается от
+// конфликта по name для понятной ошибки API/Terraform, ревью 2026-10-10).
+var ErrDeviceIDExists = errors.New("device_id already exists")
+
 // Device — устройство IoT из таблицы iot_devices.
 type Device struct {
 	Namespace     string
diff --git a/internal/service/store/devices.go b/internal/service/store/devices.go
index 73cd358..1a1ba87 100644
--- a/internal/service/store/devices.go
+++ b/internal/service/store/devices.go
@@ -6,6 +6,9 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"strings"
+
+	"github.com/lib/pq"
 )
 
 // Create вставляет новое устройство. Конфликт (namespace, name) или
@@ -26,6 +29,13 @@ VALUES ($1, $2, $3, $4, $5, $6, $7)`,
 	)
 	if err != nil {
 		if isUniqueViolation(err) {
+			// Различаем конфликт name и device_id по имени constraint (ревью
+			// 2026-10-10): PK — iot_devices_pkey (namespace,name), уникальный
+			// индекс — idx_iot_devices_ns_device (namespace,device_id).
+			var pqErr *pq.Error
+			if errors.As(err, &pqErr) && strings.Contains(pqErr.Constraint, "ns_device") {
+				return ErrDeviceIDExists
+			}
 			return ErrAlreadyExists
 		}
 		return fmt.Errorf("store: insert device: %w", err)