@yellowcat - I'm truly amazed by the effort that you are making to eavsedrop on other people's communications.

If security is what you are trying to achieve, here's a link that I posted on home Wi-Fi security with simple rules - nonbroadcasting ssid, encryption, minimal signal range etc.
5 Rules to Home Wi-Fi Security
For periodic check-ups, i would suggest that you fire up wireshark or airopeek or similar tool and do a sample capture of ongoing traffic

If your goal is constant surveillance of all traffic, you're treading on dangerous ground ...not a lot of users will be happy about it. But the best way to do it is already suggessted, stick a hub between the canble modem and the wireless router and connect your wireshark to a free port on the hub