I like the Trunk Monkey idea too, but you have to feed them.
I'm intrigued by the possibility of using old cell phones, hidden in the truck and hooked up to a permanent charging cable, that are set up with either MacroPoint or this phone app: Timed FX , for just the sort of problem you had with theft.
There must be other solutions that are meant for permanent mounting that would even alert you to initial movement.
Since I do high value sound lighting and video I equipped my trucks and trailers with lo-jac it's a one time buy and 30 to activate and track it's connected via the company to police around the country and is accurate to a few ft team tall equipment co. Have them on high theft items like generators which disappear often aroun hurricane season
yeah, I'm tempted to go that route. it would be nice to have the real-time updates of where trucks are during the day but... maybe it's smarter to separate the tasks: lojack for thefts and timedfx for drivers. I do like the idea of having an alert sent to me if anything rolls at odd hours, but perhaps I don't need it.