Here is an off-grid tracking device that lets you communicate with your group and send SOS signals even without a cell service. goTele lets you keep track of all members in your team in real-time. It works without WiFi, but you can text and track users within 3.1 miles.
goTele lets you send a SOS signal with the press of a button. The companion app lets you track all your team members in real-time and share your location. The device is water resistant too.