I need to deregister missing handset #1

First, select Deregister HS from the main menu. Secondly, press the red phone button and the # key simultaneously for about 5 seconds to finish deregistration. You will then see a message telling you to place the phone in the cradle of the base unit to register it to your unit. An "operation complete" message will confirm that the handset is now registered and ready to use. Good luck.

Getting startedReplace a handsetIf you want to replace a handset or reassign the designated handset numberof a registered handset, you must deregister all the handsets and thenindividually register each handset.To make deregistration easier, read all of the instructions on this page beforeyou begin. To deregister all handsets:Press and hold FIND HANDSET on the telephone base for about 101.seconds (until the IN USE light on the telephone base turns on and starts toflash), then release FIND HANDSET.Press and release FIND HANDSET again. You must press FIND HANDSET2.while the IN USE light is still flashing. The IN USE light flashes forapproximately seven seconds.All system handsets show CONNECTING... The deregistration process3.takes about 10 seconds to complete. All handsets show NOT REGISTEREDwhen the deregistration completes.If deregistration fails, you might need to reset the telephone and try again.To reset:1.Pick up the registered handset and then press talk/flash.Press OFF/CLEAR and place the handset back in the telephone base.2.-OR-1.Unplug the power from the telephone base, then plug it back in.You cannot deregister a handset if any system handset is in use.

If you are not too far away-not "out of range" then try rehoming/pairing the handset with the base unit. You probably need the phones together to do this. Your manual will explain how-it will have been done in the original setup.

If the handsets are not currently registered to any base, the SYSTEM RESET menu won't appear.

If the TCX905 handsets in question are actually expansion handsets from another Uniden Phone System, they are not true TCX905 handsets. To verify, remove the battery cover and battery, then look at the inside label. If it lists the model of a TRU9xxx phone system, your handsets are NOT TCX905.

Uniden unfortunately has programmed the expansion handsets from SINGLE LINE TRU9xxx phone systems to NOT REGISTER against the TRU9466. (Those same handsets register fine against predecessor model TRU8866 though).

The "END" and "#" key combination can be used for several purposes:

1) If wanting to use an ALREADY REGISTERED HANDSET on an alternate base, and if if the INITIAL BASE isn't available to deregister the handset:

1a) Press "END" + "#" until it for 5+ seconds (wait for it to beep)
1b) Choose the "Base Unavailable" option
1c) That'll deregister the CURRENT HANDSET so that it can be re-registered on ANY base.

2) If a BASE has a handset registered to it which you no longer want registered but the registered handset is missing or broken:

2a) Grab another WORKING handset which is properly REGISTERED to the BASE in question
2b) Press and hold the "END" + "#" key for 5+ seconds (wait for it to beep)
2c) Choose the "Deregister HS" menu option
2d) Pick the REGISTERED HANDSET # to de-register. (Every other registered handset EXCEPT THE ONE YOU'RE ON will appear in the list!)

Same manual as lethean provided on a similar post but Page 24 if the previously used Base is Unavailable and your phone shows "Deregistration" in the Menu.

Base Unavailable (Handset Only)
To clear the base registration data in the handset, please follow these steps:
Press and hold [] and [#] for more than 5 seconds. Select the BASE UNAVAILABLE submenu.
BASE UNAVAILABLE appears. Move the cursor to select YES, and then press the OK soft key.
ARE YOU SURE? appears. Move the cursor to select YES. Press the OK soft key.

Uniden TRU 8888Handset Reset (De-Register): 1. Remove Battery. 2. Reconnect battery while holding down "*" and "#" key. 3. Then press the right upper soft key under the LCD. 4. Press the "End" key. 5. Phone will be ready to register to the base.

If you are still looking for an answer on dereg of a handset, the manual says Menu - 0-0-2 then 3-3-5-OK then select the handset you want to cancel/deregister

I just successfully registered 4 TCX905s with my TRU8865 base - it's documented in the TCX905 manual.

Be sure the handset you want to register is fully charged.

Remove the handset you want to register from its charger.

Now unplug the AC for the main base, hold down the 'find handset' key on the base and plug the AC in again, when it beeps, you can let go of that button.

Hold down the '#' on the handset you want to register, it will show 'Registering Handset...' and when it beeps, it's done - registered, you're good to go :)