As long as you back it up with another system. I think that Clarion was supposed to debut a system like this this year, but I know Alpine has one available currently.
I put the Alpine Mobile May-Day system in the vette. Think On-Star mated to Lo-jack. The system is a satellite tracking unit. When I park the car it sets up a perimeter. IF the car leaves this perimeter without first having the key in the ignition it sends an alarm to the company and they have the police check it out. This isn't some direction-seeking system like Lo-jack either. They know (within 3 feet) exactly where you car is and how fast it is moving. So they tell the police exactly where to go.
If you are carjacked, in a bad situation, an accident, or a cop has pulled you over and you want someone to listen in on the conversation and record what was said covertly....hit the panic button. I put mine inside my shifter boot. So if I have trouble I take my hand off the shifter and viola.
The system also comes with a built-in phone. If need be you can make emergency phone calls through it. You can also contact the Mobile May Day people for directions and/or reservations at hotels, etc. And if your car is ripped-off and the people are driving they can come on and ask for the password. If not given correctly they tell the guy that the police are notified, that they know what street the guy is on and what speed he is traveling at, etc. They can also disable the car remotely on cue from any chasing police unit.
I think it is a good system. Since my car was used mostly for traveling and commuting for business I added the regular Alpine nav system in the glove box. Never had to use it much except for when in Boston or on longer trips to Raleigh/Durham, NC.
Anyway, there's my plug for the system. I haven't checked recently, but Clarion was supposed to be releasing something similar. Though at this point I may be mistaken about it being Clarion - check with your local car stereo/security gurus.
Cheers