I know that use of a camera LED and photo sensor has been discussed for triggering external devices (such as other cameras) but I don't know if this method has? :-
Use a voltage comparator across a low value resistor in series with the cameras power supply to detect the change in current when the camera is focusing or the shutter is releasing. (On mine the current increases during focusing but decreases during shutter release as the screen blanks briefly). The voltage comparator can then drive a relay etc. to trigger an alarm or activate the shutter on a bigger SLR camera (useful for giving your SLR motion detect ability). Maybe useful for people who can't use the LED method for whatever reason.
Martin.
