Power conservation mode for allowing an emergency phone call in a mobile phone

A computer device such as mobile phone device has two modes of operation, a normal power mode when available power from a power source is above a predetermined threshold and an emergency mode when the power available is below the threshold. The emergency mode allows an emergency call to be made which may be assigned to a predefined emergency call key. The power source is preferably a depleteable power source such as an electrochemical cell such as a battery. In a futher mode of operation the device is switched off when the power falls below the threshold. The device may also be turned off using a timer which is initiated when the power level falls below the threshold. The device may also comprise an external indicator which is either visual or audible when the device is in an emergency mode. In a second embodiment a second power source may be provided which is activated when the first power source falls below the threshold. Power is then drawn form the second source while in the emergency mode.