Sleep mode?

[Taucher669]

It doesn't seem they do in my case. After reading your post I've touched (backside) them to verify if they were slightly warm as usual  and they are.

You have to press the button on the rear for at least 6-8 sec until you hear a noise. Then you have switched them to sleep mode. To wake them up from sleep a short press of the same button is required. In sleep mode they are getting cold and the noise from inside stops.