I have a car with an alarm that has malfunctioned so as to go-off when ever I've pushed the lock button down manually vs. using the key-fob. I still do it inadvertantly sometimes, however.

Many times, I've set my own alarm off in a parking lot. I open the console, take out my tools, pop the hood and disconnect the battery and it resets. No one has ever questioned me as to why I'm popping the hood on a car who's alarm is going off, the horn is honking. This leads me to believe that alarms are useless as a deterrant.

Maybe some kind of silent alarm that would go off in your pocket. Maybe hooked to your cell phone?

I'm assuming that you mean some kind of spare tire that's stored under a pick-up truck, not in the trunk. Maybe a keyed lug-nut to hold it to it's storage place would be easier than an alarm?