This looks like a smoke detector but it is in fact a covert professional quality CCTV camera.
High quality 1/3 inch Sony CCD and Sony DSP chipset give excellent video results for such a unique product. They allow filming to take place in light levels as low as 0.01 lux
The unit comes complete with a mounting bracket that is attached to the ceiling first which simplifies the mounting process and allows you to have fully concealed wiring further adding to the illusion that this is only a smoke detector.
The 3.6mm lens gives a wide angle field of view, approximately 80 degrees. Try to fit this directly above the subject you are trying to film in order to capture as much detail as possible. The camera also looks downwards, as opposed to those that usually look out at an angle which aren't always ideal for till positions.
This camera has been used successfully located above till positions to see both customers and shop-workers hands going in the till when, as a shop owner, you would rather they didn't! Because of it's appearance as a smoke detector there isn't a problem with the camera being fitted close to the subject being filmed.