Everyone knows the importance of UHF/VHF bands height to communication distance and effect. On the top of the mountain, it is possible to communicate with quite distant stations with only common handheld radio. 

A repeater radio is simply a device that amplifies the signal transmitted by a low power (2W-5W) handheld radio and then sends it again with a high power (20W-50W). This achieves a larger coverage area and greater penetration of the radio wave transmission. Of course, in order to save power consumption and extend the life of the equipment, it is important to avoid transmitting useless waves as much as possible. Most amateur repeaters use CTCSS (Continuous Tone Coded Squelch System).

So how does a walkie-talkie know if there is a local repeater?