radio, cell phones
The monitoring device is a radio transmitter that sends signals to the radio transmitter. Radio waves are a type of Electromagnetic waves.
Quasars
radar
amplitude modulation
radar
radar
A pulsar.
radar
radar
You may be thinking of weather RADAR. It sends out radio waves, some of them bounce off of rain, snow, or the boundaries of layers in the atmosphere, and the radar receiver detects the waves that bounce off of something and come back.
It is receiving the waves from radio or television stations who send them troughout sending devices. A radio station for example will have a tower which sends these waves up to a certain distance radius.
A Wi-Fi router modifies the waves it sends by encoding data onto radio waves and transmitting them through antennas. This process involves changing the frequency, amplitude, and phase of the waves to carry information.