Lorex is one of the top providers of security and surveillance equipment. Here is an example of one of their black and white wireless systems. They offer high quality color systems with monitors so you can keep an eye on everything that you are missing.
Consumer Price: $79
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PDF Spec Sheet

2.4 GHz WIRELESS B&W

. Turns your TV into a Video Security System
. Install and Operate in less than 1 minute
. Flexible - move camera from room to room
. Listen-in audio
. Auto scanning - up to four cameras
. Camera with AC or battery option
. Selectable auto or full screen options
. 300 ft wireless transmission(open space)
. Record picture to any standard VCR
. LED indicator lights show system status
. Compatible with all Lorex 2.4 GHz wireless devices
. Connect up to four cameras
(additional cameras sold separately)
. System includes: 1 B/W wireless camera,
wireless receiver, 2 power supplies, RCA cable