diff --git a/src/services/NotificationService.ts b/src/services/NotificationService.ts
index 76651bd..a223e89 100644
--- a/src/services/NotificationService.ts
+++ b/src/services/NotificationService.ts
@@ -77,6 +77,7 @@ export class NotificationService {
 
   private async etaSubscriberCallback(eta: IEta) {
     const tuple = new TupleKey(eta.shuttleId, eta.stopId);
+    // TODO: move device IDs object (with TupleKey based string) to its own class
     if (this.deviceIdsToDeliverTo[tuple.toString()] === undefined) {
       return;
     }