An image monitoring system uses wireless communications to transmit images for security monitoring. The system includes a central controller (105) and a plurality of digital still camera units (110) operatively connected to the central controller (105). At least one of the camera units (110) includes an image sensor (215), a motion detector (220) that causes the image sensor (215) to receive image data when motion is detected, a micro controller (205), and a first nonvolatile memory operatively connected to or included in the micro controller (205). The micro controller (205) determines whether received image data should be transmitted to the central controller (105), and the central controller (105) determines whether received image data should be transmitted to a monitoring station (115). The camera units (110) may further be used as standalone units as replacements for motion detectors in existing security systems.