PURPOSE: To prevent the generation of a stray child in advance by providing a base unit and a slave unit, providing the radio transmitter of fine transmission power in the slave unit and providing a receiver and an announcing means, which announces the strength of a signal received from the slave unit, in the base unit.

CONSTITUTION: A base unit 1 is provided to be carried by a partner, and a slave unit 2 is provided to be carried by the child to be confused in getting lost. The base unit 1 inputs an incoming call signal to an antenna 3 through a receiver 4 to a code decoder 5, analyzes it at that site and operates an announcing means 6 when no signal is not received from the slave unit 2 as the result. The slave unit 2 is equipped with a transmitter 7 and an antenna 8 for transmitting weak radio waves and a code generator 9, which modulates a carrier by a specified code signal, is connected to the transmitter 7. Thus, it is detected that the child or the like is away from the partner, and by announcing it, the generation of the stray child can be prevented in advance.