A security device for detecting the position of a manhole cover includes a pinger device, such as an acoustic pinger, that transmits a signal in the direction of the expected position of the manhole cover. The device takes energy samples to determine if the signal has been reflected back by the manhole cover. If the device determines the signal has not been reflected, it determines that the manhole cover has been moved from the expected position. In response, the device captures an image of an area around the expected position of the manhole cover. In addition, the device can notify a remote security station via a network that the manhole cover has been moved.