I use a Gorilla alarm with a pager (model 8017). It may not stop a thief, but it gives me piece of mind knowing the pager has not gone off. If I am nearby, I don't bother with the pager, I just set the alarm.

For fun, I added a two level proximity sensor. The outer perimeter just beeps lightly if you get real close. If someone tries to mount the bike the tighter perimeter triggers the alarm. It doesn't need to wait for a tilt or a bump.