Efgeeco Optonic Bite Alarms

Here are a pair of Efgeeco Optinic bite detectors. They were purchased new by me in the 1980's.  There are 2 models.  There is a Super Compact (VTVCL) and a Special Compact -LO (STVC-L).  The Super Compact has a variable frequency control as well as variable volume control. The LO is a fixed frequency alarm  with a volume control. Both are working well and are supplied with 2 new 9v batteries. I have filmed this. Both have 2 and a 4 vane paddles.