Sounds like you don’t need a technological solution but a social one.
Have them check in a personal item to receive the forklift keys such as their wallet, photo ID, or car keys.
And it’s free, just slower and requires some paperwork.
I think a LoRaWAN based tracker might be perfect for you. I've been keeping an eye on the Loko myself:
Neat!
Closest thing I can think of something using GPS and radio communication, but the only context I've seen or looked for it in was for finding rockets. I recently bought a kit from eggtimerrocketry.com that does not require a radio license, but there are also systems out there that require a 60mm HAM radio license. These may be too bulky or take too much assembly for your need though, and I'm not sure about battery life as they are intended for relatively short rocket flights.
The loko beacon posted by someone else looks to be similar and pretty good, not sure if it uses the same tech or not tho.
You could do something with LoRa
But I agree with the other poster, a social solution is better than a technical solution. Make them leave something of theirs. Car keys, phones, etc
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