If you buy the headset only (without the base), it must be synched to the base you use it with. My original one that came with the base fell apart in my hands one morning after 4 years of daily use. I thought I'd save money buying just the headset part I needed since the base I had was working fine. Couldn't get the replacement headset to synch at all to the base -- tried a variety of ways to get it to work and multiple attempts. The directions were pretty precise so not much room for misinterpretation. Just didn't synch -- so basically, these were useless new headset replacements. Ended up buying the whole unit (headset/base) and only got to keep my original lifter functioning without replacement. Good to go now. Don't waste your money - just buy the base and headset "combo" when you need to replace either one.