IMO the DEI Viper car alarm is the best. I would say try to get a viper 300. The brain box is small enough to hide on the bike and the add ons you can do are limitless. With a bike application you will only use about 4 of the 9 or 10 wires. For the tilt option you can get a mercury switch and put it somewhere when the bike is put upright it will be tiggered. The brain box has a built in shock sensor also. And starter disable.
The pager add-on brain box is a bit larger but is still hideable. As for bike alarms I'm not sure. Scorpio are the best ones, easy to install, but very expensive($250)(w/ pager $360). Gorilla is a simple alarm($87) but the siren is built in and you can't add a pager.
The viper 300 is a little over a $100 w/o install(If bought from a shop). Check out ebay for these. Most shops won't sell you just the alarm without install, unless you are certified, cuz DEI won't warranty the alarm if somone who is not certified installs it. Pus the shop makes no money.
this is one link for ebay:
Hope this helps! :thumbup