What I don't get though, even after Joe's explanation, is that the Extender which sits next to the laptop is ALWAYS stronger by far than the original modem, yet it switches every day back to the modem. Again the modem, is never stronger. And it never switches back to the extender. So that is baffling.
When you say "never" I presume you are using some type of recording signal strength meter that is sampling say 60 times a minute 60 minutes an hour and 24 hours a day? The Netspot app you are using has a minimum scan interval of ten seconds. It only takes a drop out of a second or even less to cause the switch. Is it possible your extender is set to renew its IP address lease from the router every day or your router is set to renew all device IP addresses every 24 hours? That could do it.
As far as switching back to the extender, once connected to the router the only reason for the laptop to switch back to the extender would be if the router signal were interrupted. Try unplugging the router and see if your laptop switches back to the Extender. Depending on what services are actually provided by your externder, that might or might not work but it would be interesting to see if it would.
