TriggerTrap is an iPhone/iPad app that works in conjunction with a special camera connection cable to trigger DSLRs in a variety of different ways. There are 12 different triggering modes, including two different flavors of timelapse, distance-lapse, motion detection, sound, magnetism and vibration sensors, and a facial recognition sensor.
Virtually all of the recent Canon and Nikon DSLRs are supported by TriggerTrap. A number of other models from Sony, Hasselblad, Pentax and others are supported as well. There is a full list of supported models on TriggerTrap’s website.