Clarity D613 - Manual (Page 14)

D613 HS
Additional Handset
The D613 will support up to 5 handsets. The D613HS is an expandable handset
that is sold separately.
Registering Additional Handsets
1. Press and hold the FIND button on the base for 4 seconds.
2. Release the FIND button once the IN USE light starts to flash.
3. A confirmation tone will sound when registration is successful. Handset X is
displayed where X denotes the number of handsets. The phone will then go
back to idle.