A power management method for a handheld mobile computing and communication device for a normal and an emergency occasion is disclosed. The device, for example, is useful for a trapped person under a mound of debris created by a fallen building during an earthquake or a terrorist attack. The invention is based upon a conventional mobile communication device with a second communication unit and a sensory unit. The second communication unit is based upon a short-range and ad hoc communication network. The invention is characterized by that a power management unit is used to monitor the remaining power of a battery system for the mobile device. If the power is below a preset threshold, the main function of the mobile device as a mobile phone is switched off and the reserved power is used to supply power for the second communication unit, which consumes much less power, in particularly, in a mode as a receiver only. An authorized signal, delivered by a nearby mobile rescue station and received by the second communication unit, will trigger the power management unit to provide additional power to activate the sensory unit. The sensory unit such as an accelerometer and / or a gyroscope may detect a signal if the person touches and / or moves the device after receiving a triggering signal. Yet additional power is further supplied to send collected data through the second communication unit to the rescue station.