Rowe et al. in their paper [7], convey that camera
surveillance raises many problems. Visual surveillance is
difficult for this task. Most emplacing is at night, and infrared
cameras are expensive when covering tens of kilometers of
road. Cameras are hard to be concealed, and suffer problems
with occlusion (whether deliberate or accidental). Image
processing can be unreliable with weak or distant signals, and
privacy is more extensively invaded with camera surveillance.
An alternative for detection of suspicious is passive-infrared or
magnetic sensing. Change-detecting sensors are common in
automated surveillance tasks, and they can use several
modalities. They can be inexpensive and have low power
consumption because messages need not be transmitted unless
evidence of change is strong.