guess it's good if you're going to beyond earshot of the siren, having the pager, but i think in most cases, just the siren would suffice. Here's one for $20
Guardian ALARM for Guardian Motorcycle Covers: BIKEBONE Even if you were beyond earshot of the siren, when that goes off, any thief is gonna drop tail and boogy.
btw, I have seen pager alarms with remote start and kill built into them for that price.