These are cheap disposable audio beacons with foam tape backing that run on the same batteries that they put in audio greeting cards. The beacons could be made to last for a few hours. These could be used for events where blind people are going to need assistance navigating to and from the event, for instance from the subway to a meeting place and back when the path is not straightforward when navigated by cane or dog alone.
-- JesusHChrist, Jun 02 2013

random, halfbakery