http://www.pieps.com/cms/media/manuals/pieps-manual-de-en.pdf

IMPORTANT! All participants (including
observers) must switch their devices to receiving
(SEARCH) mode. Always make sure there are no
electronic devices (e.g. mobiles, radios,) or solid
metal items in the direct vicinity of the search. Due
to the fact, that the beacon is not transmitting a
signal in SEARCH-mode anymore, the PIEPS DSP is
equiped with a rapid switch-back mechanism (just
push on the protruding top of the main-switch) in
the case of a following avalanche.

Regards,
siroco