Yes, but the electronic detectors (mine's a Snap-On!) are notorious for false alarms.

The problem is that the detectors detect all kinds of chemical compounds that are NOT R-12 or R-134a. I can make mine go off by burying it's nose in the carpet; I think it's the vinyl chloride (new car smell) that causes it to beep.

Dye is almost foolproof. The only thing that can trip you up is if the valve where you added the dye is leaking. Clean off the valve after you add the dye; it it comes back, you have a leaking valve.

Nate