GPS trackers, mains power or battery, low cost?

Has anyone got experience with GPS trackers? Can be wired in or battery powered, sim card, discrete?

Most of the units we've seen are proprietary and expensive or designed to just have one or two units to monitor. We need 300+ which also means management will be tricky. Our units are to recover stolen property, not for day to day tracking but they'd still be expected to "ping" at least once a day.

 

We mostly need to track movement and to have a system that alerts us of that - but with 300 we can't look at a map and think "everything is where it should be".

This is an old map of just our Auckland cabins - we have more now, and covering all this map. If something in that cluster moved we'd never know without an alert, but we don't want to be bugged by authorised moves.



Friends with their own cabin business had one stolen recently and thanks to a sharp neighbour they learnt the name of the trucking firm that was used, from there CCTV and GPS tracking of the truck means they got the cabin back and there's a truck driver looking for a new job. We can't rely on neighbours, though, but we also can't afford to blow our costs out.