nice idea..excellent customer service..but advised after testing by representative not compatible with some wireless phones...unable to turn off ringers..so each call would ring 6 times before message. This is the second unit in 4 days...the first same issues.
I receive a dozen + robo calls a week...so we leave the phone off hook unless we call OUT.
Will be setting up the answering machine on our wireless for one ring..request LEAVE A MESSAGE..WE WILL RETURN YOUR CALL....
Robo calls are taking over these days..most all 100% are crooks and thief's that want your credit card numbers...were in our senior years..difficult to walk to countless worthless phone calls that only want to scam and steal from us

I was getting 5-10 robocalls per day. As both my wife and I are mental health professionals, this meant we had to check the caller ID on each call. Since the robocalls spoofed area numbers, we often picked up the call. Now, not a single robocall gets through. None. Zilch. No ringing phone that we need to jump up to look at only to have another robocall. We simply added the people we wanted to the white list, real people can get through the screening system. This thing works and works well. Everyone that gets through wants to know how to get one. Peaceful bliss.

Update: I turned the unit off for a day to receive an important call. Immediately the phone starts ringing with robocalls. I had forgotten how effective this is. I didn't need an alarm clock, the first call came at 8:01 am.

One characteristic of the unit to work around. If a first time caller presses "0", their call does not go through, but instead goes to the unit's answering machine. A dim LED alerts you to this. The unit's answering machine does not have good voice quality, it is difficult to access from the unit, difficult to clear calls, and no remote access is possible. The recommendation from another user to replace the outgoing message with telling callers to press "0", hangup, and call back is a good alternative. That way callers get through to you or to your standard answering machine.

Even with the quirks, still a 5 star -- peace and quiet!!!

I hesitated a long time to buy this device because of the vague comments about compatibility with VOIP. I don't know how life is for you, but I was receiving so many daily spam phone calls that I was becoming very frustrated and angry. As an act of desperation in an effort to find relief, I decided to take a chance on this device's compatibility my internet phone provider . The device arrived ahead of schedule from Amazon. It was easy to install between the Spectrum cable modem and my Panasonic cordless phone base station. It requires no external power source but is dependent on internal AA batteries (not included) to retain memory. The device is non-intuitive to operate the first time, but the included simple instructions are easy to follow. With experience, placing spam on the REJECT list will quickly become fun and personally satisfying. Any phone number already placed on the ACCEPT list will be completely transparent to an incoming caller. Any phone number not already on the ACCEPT or REJECT list is placed on a list of incoming calls awaiting your disposition (who shall I reject today). I set-up my Sentry so that any robo-spam numbers not already on the REJECT list will not ring-through to the phone. It is interesting to me that the instructions refer to the ACCEPT list as the "white" list and to the REJECT list as the "black" list. Yet, the buttons on the device itself are green and red, respectively. Go figure. The answer as to whether or not Sentry is compatibility with your VOIP provider is still a vague. My Sentry works flawlessly with Spectrum. Subsequent to the installation of this device, spam calls ringing-through into our phone came to an absolute screaming halt.This device has returned to me control over my own phone. I cannot recommend it strongly enough. As I was writing this review, an incoming number already on the REJECT list arrived and was promptly disposed-of in seconds. It was so cool to watch. The silence is golden!

Unfortunately this didn't work for me. The manual could have been a little more detailed but initial setup was easy. I used my cellphone to test and enter my cell number for the black list and it failed to block and didn't show caller ID number. The ringer is very loud with no volume control and it will ring 9 times before the answering machine picks up. There is no setting to control the number of rings and I would think most people would hang up after 5 or 6 rings, this to me makes the answering machine useless. I prefer to use the answering machine on my V-tech cordless phone but the only way I could do this was to turn the Sentry unit off which defeats its purpose. I cannot recommend this product.

Well worth the cash. I was getting bombarded with spam calls, plus scam calls as well. Hooked this baby up and fixed the problem immediately. This machine was blocking about 14 unwanted calls a day at first. After a couple of weeks now its down to about 4 a day. I have not had a unwanted call get through yet. The pre-recorded message tells the caller to remove my number from their list and to hang up. I'm not sure if my number is being removed from any list or not, but the volume of spam calls is way down now. Not a single spammer has dialed "0" yet to get through. I also have not missed any calls that I wanted. This machine is pure genius. As others have mentioned, the documentation is pretty worthless. I was a bit puzzled for a brief moment when setting it up. Something about holding a button down for 2 seconds, and I was pressing the button, or holding it too long. I figured it out eventually, I don't even remember exactly what I was stuck on at the time. I found the answer on their web site. The spammers use robocalling machines to bombard us with unwanted calls, now I have a robocall blocker to thwart their efforts. So far it has done just that perfectly.