Home FAQ Will the OnStar Guardian app work if I don’t have a cellular signal? No. The Guardian app needs a cellular connection in order to connect with OnStar. Should you encounter an emergency requiring law enforcement, EMS, fire or other emergency services, always call 911 first. Previous Why does the OnStar Guardian app need access to my Microphone, Location and Notifications? Next Does the OnStar Guardian app replace my current OnStar Safety & Security Plan?