Overview of the full aftermarket car alarm security system that was installed in a 20yearold Jeep Wrangler:

Viper 3305V 2way alarm system with pager (~$120)
Directed Electronics Dual Zone Motion Sensor 508d (~$32)
Directed Electronics 507M Tilt Sensor (~$28)
Directed Electronics 506T I.T. Audio Sensor (~$16)
Security Hood Door Pin Switch (~$7)
Local installation ~$100 (for time/labor); took ~2hrs to get all the components installed at a local shop.

Pros:
far more effective than a stock car alarm at detecting and deterring car theft/burglary
the 2way pager alerts you of car alarm sensor activation if you're too far to hear it directly (pager works up to ~2 blocks away in a city)

Cons:
$ costs of system + installation (above are the prices I paid)
would've been too complex for selfinstallation (for me personally, because requires running wires through dashboard and firewall to engine bay)
slow battery drain if you leave the car in a parking spot with all the alarm sensors activated (without starting the car to recharge the battery via the alternator), my car battery only lasts ~23 weeks before car battery dies, so I make sure to start the car at least 1x/week to prevent this if doing longterm parking with the alarm on; battery drains faster obviously if it's colder outside and if the alarm keeps getting setoff by sensor activation

Overall I think it is an excellent choice as an addition to or replacement of stock car alarms and am happy I had it installed on 2 cars now. The Viper alarm functions fine without the accessory sensors, but adding additional sensors definitely improves in theft detection (especially the tilt sensor and the glassbreak audio sensor).