@ducktech 

Open the Deco app, go to More > Wi-Fi. If security is currently set to none, change that to WPA2-PSK [AES], you will be able to set a password as well.

@Tony 

That's the problem, I've set the password from the very beginning.  Also tried changing the encryption type as well. The last thing I've tried is turning on the guest network. Not quite sure, but that may have forced the password to be required to get on main network. Still not sure that's the correct way to do it. 

@ducktech 

That should not have been needed, but odd how that forced it. By default WPA2-PSK (TKIP/AES) should have been selected for the main network.

@Tony 

Unfortunately, it still isn't right. My father-in-law's watch joined network without need of password. Kinda don't know what to do about it. 

@ducktech 

If a device has joined another network with the exact same credentials then it will connect to another network even if it is physically different. It sees the same name and will provide the same password.

Go into your Deco app, and go to the wireless settings, and change the network name and password to something completely different that is unique from past network names, as well as the password.

If you then look on your smartphone, see the available wireless networks, you will see a lock indicating a password must be used in order to connect.

If you still have connections I would recommend reaching out to our support to go over your network as there may be an existing network aside from the Deco that is connecting or something else that is on the network we may not be seeing: link