Phil-CCTV

I need to setup a camera focused on one specific cabinet in a bar. The camera needs to be activated when somebody opens that cabinet and shut off when it gets closed or 30 seconds after closing. I have a few cctv cameras already (from a different application and now un-used) but no DVR. I was wondering if there was some sort of wireless magnetic relay activation that could be used with a PC running some sort of recording software. I'm looking for ideas at this point since motion activation of the camera would be ludicrous. I'd be going through 18 hours of video a day to try and find the right 15 seconds. Unfortunately, the location of the cabinet precludes cables to it. Any ideas at all would be very welcome. Thanks in advance.