The trick is to install the devices. It's their island and they probably know every inch of it. How to land on the beach, sneak around and plant surveillance

The trick is to install the devices. It's their island and they probably know every inch of it. How to land on the beach, sneak around and plant surveillance devices (that ideally are solar powered and broadcast their data to some offshore station), and get off undetected? And hope the devices aren't discovered and tossed into the ocean? Also, the equipment would need to be totally sterile. Mighty though our civilization is, we lack the technology to spy on an isolated Stone Age tribe like this. Rather humbling.