Thanks for the details !
In this context, a "PIR" is a Pyroelectric Infrared Sensor, of the sort that are built into simple motion-sensing
and occupancy sensors of all sorts. I have one that turns on the lights in the washroom at work, and two
that light up the path and doorway when I get home at night.
Controlling an external beacon with one of those switches is a trivial task as long as the voltage and current
of the PIR sensor are compatible with the beacon. A quick Google search finds 12V to 24V compatible ones for $10 USD.
Connecting a discrete input to an RTU or radio telemetry system is a much bigger question.
Do the trucks already have telematics ? Do they use your local cellular phone networks ? Are there auxiliary inputs in those telematics systems ?
What sort of "Server" do you want to communicate the truck occupancy or other information to ?
Is there other truck information you want to send to a central server, from the engine or HVAC or fuel or payload or GPS location ?