I installed a Viper alarm on my previous car and it was a horrible mistake. I paid I think $130 for alarm including install. Turns out the shop was a sh1t-shop from craigslist and the alarm was installed in a lazy manner. They did not stuff the brain deep enough into the dash and a thief could easily reach in and yank out the wires quickly. They also set the sensitivity way too high and the damn alarm would get set off even by the UPS and Fedex truck as it drove by. Also when a school bus drove by or Ice cream truck. I started to become very unpopular with the neighbors.
I went to the shop 3 times (a 30 minute drive each way) to have them adjust the sensitivity but I dont think they did anything at all because problems persisted. In the end I deactivated the alarm and left the fob at home. It was a waste of money. The best deterrent is just not to leave anything laying around that a thief can see when peeking in the window. Plus having a stick-shift car is a great way to thwart thieves in the USA since almost nobody knows how to drive them.
I went to Benihana whcih has mandatory Valet Parking and the numbskull driver drove the car with the parking brake still engaged. I was so furious I wanted to punch him in the face. I dont get angry easily but I still remember that day.