Just go for a regular alarm with backup battery and a backup siren maybe. I don't see any advantage for the pager alarms over the standard ones. Heres what I think of the paging systems. The pager alarm has 3 scenarios. Scenario 1, the alarm is going off but the owner is off watching a movie so the paging feature doen't reach, returns to the stall only to see that your car got stolen. Scenario 2, the alarm goes off so the owner runs out, beats the crap outta the thief and saves the car...highly unlikely unless you are Jet Li or own a M4A1. Scenario 3, thief and his gang of thugs know the owner has a paging alarm, kicks the car and waits until the owner shows up, kick his butt, robs him, then drives off in his car using his own keys.
Just buy a good alarm system from a popular company, viper, dei, clifford, alpine...along with good insurance. If someone wants your car bad enough they'll find a way to take it.
-hawaiian