Wireless closed circuit system recs

My grandfather says someone is knocking on his door at night. I'm looking for a wireless closed circuit security system. I only need one camera for the front door. He has a security light right outside the door which could provide power to the unit we eventually purchase. He is not interested in an alarm, but for something to notify him if there is movement at the door.

I know a Ring Doorbell would accomplish this, but he is looking for something that would display on a monitor what the camera is recording 24/7 and kind of buzz when there is motion. The unit not being wireless is not a deal breaker.

Any recommendations?