3.  Every cell phone puts out a frequency.  Large areas of land are broken into smaller pieces so frequencies can be reused in many areas called channels.  CP compared to a walkie talkie?  Each conversation has 2 frequencies, a frequency you talk on and a freq you listen on.  Channels - A walkie-talkie typically has one channel, and a CB radio has 40 channels. A typical cell phone can communicate on 1,664 channels or more!

5.  Uses infrared frequencies as a pulse. Different pulses means different things like on/off, ch +.  There are filters and certain ranges that are set aside for different remotes. The filters block out other frequencies from interfering with it.

6.  transmits high-frequency (1 to 5 megahertz) sound pulses into your body using a probe.  The sound waves travel between fluid and soft tissue, soft tissue and bone.  Some of the sound waves get reflected back to the probe, while some travel on further until they reach another boundary and get reflected.reflected  The reflected waves are picked up by the probe and relayed to the machine.

8.  The military has developed weapons that use sound to stop enemies.  “Mobile sonic devices” produce high frequency sounds that only teenagers can hear.  A powerful ultrasound gun can liquefy living tissue.  A low frequency can make a building collapse.  A vortex ring can knock a person over.