Heres my opinion on alarms.

From best to worse
Phantom,
Lo jack,but has no siren or sensors.It just have a GPS,that your local police,sherrif.or state trooper can track after you activate it.Also not all cop cars come with lowjack tracking divice,but each department do have cars with it equipt.(Info from my cop neighbor.

Scorpio,only think I dont like about this alarm is.
It does not have a flashing LED,and only comes with one remote.

...

The next 2,im not sure which ones better.
Gorilla
"Merlin" bike alarm from Viper.

You all know on alarms,you can have a few "upgrades"

and yes,any alarm is better than nothing.

Ask the people here who have had thier bikes stolen,if they had an alarm on it.I bet most of them dont.Any alarm or any of the security systems listed ablove cannot garentee 100% that your bike wont get stolen.