【Block NO CID Calls】Important Note: This product requires Caller ID service from your network provider. Enable “NO CID”function, All unavailable, private, anonymous, name not provided, unknown numbers and calls with no Caller ID will be rejected. | 【Create Blacklist】UP to 4000 unwanted caller numbers blacklist, you can add phone numbers to your blacklist in a variety of ways, whether it's one-touch blocking on incoming calls or adding numbers manually. | 【Incoming call logging】when the landline phone receives an incoming call, this call blocker will log the number so you can identify it. You can also manually delete or blacklist the number. Note: if you delete a blacklisted number, it will still be blocked. | 【Easy to connect】Need an short RJ11 cable (included in the box) to connect this call blocker to your landline phone, no need for batteries or extra power supply. If no ringing tone or intermittent ringing issues arise, try a phone line splitter to connect. Meanwhile the lcd screen has 5 levels of adjustable brightness, choose the one that suits you best. | 【compact and lightweight】This call blocker for landline is compact and lightweight, 3.3*3.5*1.6 inches size makes it suitable to be placed anywhere in your home or office. You can place this call blocker next to the telephone to maximise space saving and get the best experience.