You DID try to find the manual (REALLY easy to do online) and read it, didn't you?
Out of range warning:
If you hear a warning tone during a call, and/or the sound in the earpiece becomes faint or distorted, you may be going out of range of the base unit telephone. Move nearer to the base unit telephone within 20 seconds, until the tone stops. Otherwise, your call may be cut off.
While you are out of range and you are not on a call, the handset's display shows SEARCHING and the signal level symbol flashes. Before you make a call, you must move closer to the base unit until the handset's name and number are displayed and the symbol stops flashing.
Of course, if the main base unit is not powered up, that would have the same effect.
Manual available here ,for those incapable of doing a Google search:
http://www.manualslib.com/manual/249919/Binatone-Symphony-2210.html
XX, October 2015
