1.   A cellular phone is really a mobile radio system that sends a signal out over public airwaves.

2.   A transmitter connected to the door bell sends radio signals to a portable receiver.

3.   If the total strength of the input signals exceeds a certain threshold, the unit sends a signal on to other units.

4.   In addition he or she could see smoke signals sent from island to island.

5.   It has sent signals that the Tories never would.

6.   Radio signals were sent into deep space.

7.   They test their models by sending signals back through the electrodes and observing changes in behavior.

8.   When the stereo sends audio signals to the electrodes in the speaker, sound comes out of the perforations.

9.   If a problem does occur, a signal is automatically sent to the mainframe.