Viper and Clifford share only 1 same line, the pager alarm. Which is the viper 791xv and the clifford matrix. I don't know why DEI did this but they're the same exact thing.
Clifford's Intelliguard series is by far the most advanced of all the DEI products. DEI did buy out Clifford a bit ago and they might be incorporating Clifford's technology into current Viper products. But if you compare any of the Viper alarm systems features to the Clifford Intelliguard or Avantguard, you can see Clifford is better.
One of the most important key features that Clifford offers I think is their wireless immobilizer. "Wireless Immobilizer interrupts yet another vital engine point, such as the fuel pump or fuel injection system, and does so without any wires for the thief to trace! It’s completely user-transparent, so there’s nothing special you ever need to do."
But all in all, if someone reallllly wants to steal your car, they're going to do it with or without a good alarm.
im an installer at circuit and the reason we are going back to dei is because the alarms that replaced our viper line was code alarm... PIECE OF SHITTTTTTT!!!!!!! we had nothing but problems with those. i think circuit was trying to save money by switching away but they lost more money going with crap i mean code.... as far as dei's best brand... there is none. they are all the same. i just swaped my old viper 690 for a new python 881xp. i had to do no additional wiring. the plugs are all the same!! dei is lifetime warrenty too so if you have problems take it back...