Fingerprint readers in that situation are really expensive and easy to get around. Someone could kick the door in and you'd still be none the wiser. Ideal solution is to use a camera that can cover the whole area. Mobotix Q24 gives a 360 degree angle, so can cover several cubicles from the outside. Obviously you need to be careful with placement, but we have had considerable success in schools with this sort of problem. Other benefits are the camera is self contained, can sit directly on your network, is powered by PoE and comes with free software. Oh and the picture quality is like watching TV.