An emergency mode is provided in a portable electronic device for locating a survivor in a disaster. The device includes a wireless antenna to transmit and receive wireless signals; a memory to store one or more identifiers; a user interface to receive a command that enables the emergency mode. The device also includes one or more processors, which, in response to the command, detect via the wireless receiver a predetermined identifier that matches a stored identifier identifying a sender of the predetermined identifier as a trusted node. When the predetermined identifier and a timing measurement frame are received from the trusted node, the device sends a response to the trusted node to indicate its presence.