Amps that switch on when receiving an audio signal

I see that there are power amps from Cambridge Audio and Parasound that switch out of standby and into operating mode when they receive an audio signal. This seems to me a pretty cool feature -- cool in more ways than one, of course. (Energy saving, etc.) Are there other amps that do this? Are there many? Is this becoming something of a commonplace and I'm just now noticing it?


-- Howard
My Rotel HT system does .
JL Labs subwoofers have a setting that does this.
I have an old Harman Kardon amp from the mid 90s that has that option.
As for subs, most powered subs offer this option.

A while back I bought an amp on ebay (can't remember the brand) that was listed as "dead" for parts only. When it arrived I noticed it had an auto on switch. I turned the switch off and the amp worked great. After some research I adjusted the auto on trigger and that worked great also.
Not really important no great amp have this.
My Sunfire 300 only uses 20...25w stand-by so no need to switch on-off. It stays on 24/7 and always ready to blast music.
My Sony does, and also turns itself off with no signal after 15 minutes. Utterly love both features. I hit pause on the Sony server when music is playing, leave the house, and both units auto shut off.
The (low-end) Sony subwoofer I use for home theater does this and it's a real bother (relay is very noisy).
Frequently clicks-off when no LF present in program.

Another function I've seen is auto off-on (Pretty sure my ARC VT-100 had this). A control cable is used to turn amp on-off depending on the state of the pre-amp.
"Not really important no great amp have this."

Important to who?

Its a nice feature if one cares. Some do apparently. I would not mind having it if all else is in line as well.
Outlaw M-2200 monoblocks.
My REL is important dammit...and it has that feature working perfectly for years, although if it wasn't I'd be unhappy...because it's so important...
Now I want it for my amps. Damn!
I already have the ridiculous hassle of having to hit the "warm up" tube power amp switch after the power conditioner start sequence. That's at least 10 seconds a day that I'll never get back...