There seems to be new boxes with two black circles or holes that have been installed over the rear door exit near the Emergency Exit panel, in a few of the modern buses (MANs and Scanias)
I've only recently noticed them, but I have no idea how long they've been there.
Anyone know what they're for?
You will also find the same equipment above the front doors.
Refer http://www.actbus.net/forum/index.php?topic=3742.0