flyback/snubber diode in relays

To all the pro installer, Do you always use snubber diodes in relays? http://en.wikipedia.org/wiki/Freewheeling_diode

always, always without exception? No. It depends on what is "triggering" the relay.

Let's say one end connects to 12V+ and the other connects to a neg output signal from alarm system.

Probably yes unless you know if what is "triggering" the relay tolerates the relay. FWIW - I never use snubbed relays - I add external diodes etc to plain relays.

During the 7 or so years I installed alarms/remote starts for a living I don't think I ever installed a diode across the coil of the relay. There was an occasional unit I purchased that had the diode preinstalled, but that was rare as well.

Example. . . Alarm (+) trigger to power locks. Diode? most likely no. unless 07 or newer car. Alarm (-) trigger for say a GM reverse polarity power locks. HELL YES. Its situational. It basically avoids that voltage spike when the relay lets go.

I, too, never added a diode to a relay when installing alarms. Any respectable alarm will have the diode built in to the (-) output.Kevin Pierson

Just about all alarms that have a 200Ma output are expecting you to use that wire to power a relay.  Most of them have diodes across that wire to the power path. 

The backlash from a relay is sometimes severe.  A transistor or logic circuit that is only capable of 200Ma wouild not survive for long without a diode across it.   They know that they can not count on everybody installing an alarm to install a diode.  They put the diodes in the alarm brain.

 EDIT: I did not see Kevin's post, so just like Kevin said.

Kevin is right, but the same goes for any respectable anything - they should be self protecting (withing reason). (At first I was going to disagree, then I re-read and realised Kevin wrote "Any respectable alarm will have the diode built in..." - not "Any respectable relay will have the diode built in...". The latter I do dot like!) Keep in mind, the protection is for voltage spikes (not current surges etc). As icearrow wrote, they are essentially when the coil de-energises, hence a HUGE negative spike that reverse-biases & fries electronics, and that's what the reverse-biased diode "quenches". Varistors would be required for positive spikes, but they are rare.

From what I understand is that the collapse of the magnetic field would cause induced voltage greater than 12V+ so current will flow toward the 12V+. Would this cause any damage to other components in the car that connects to 12V+? BTW, I have the viper 5901.