Handset out of range - Uniden DECT 6.0 Cordless Phone ID

I'll give it a shot. Have you tried re-regestering the handset? Press and hold down the "end" key (on most models it looks like a red handset) while holding that key down, press and hold the # key, after a few seconds the unit should beep and show:
(SYSTEM RESET)
Deregister HS
BaseUnavailible

Useing the four-way key select "Base unavailable" and press the menu key The LCD display should then show :
"Which Base?"
Base #1

Select base one and then the display will show
"Base Unavailible
Yes
No

Select "Yes."

Your handset is now unregistered. To re-Register the phone to the base do the following. If the base unit has a charging cradle, just set the handset in it and it should register on its own, if you have a cordeed base, or the unit will not register when you set it in the cradle on the base go to menu and select register handset, then press and hold the # key on the handset for 2 - 3 seconds, it should beep and then start the registration process. If you have 6 handsets registered to your base, you will need to de-register teh non-working unit from the bases memrey before you will be able to re-register the handset.

After doing what Guru says to do if your unit doesn't re-register, then, if you have a base unit that plugs into an outlet, unplug the line on the back of the unit next to the telephone line. Before plugging back in hold the on-off button and the clear button (the circle with the line through it) down and plug the line back in at the same time. A "P" should flash on and off and the 0 showing no messages will come on. Set the handset in the cradle and it should now reset.

If you are with in what you think is a reasonable range ... your batteries are probably just about done for ... replace your batteries.