What to do:
Keep an inventory of your devices, and the devices you have that are connected (or need connection) to the internet.
Why do it?
Devices that need to connect to the internet in your home include PlayStations and other video gaming systems, Smart televisions, Smart thermostats, refrigerators electronic door locks and video surveillance cameras.
An inventory allows you to spot if a strange device has joined your home WiFi.
You should also change all default login passwords and check periodically if the manufacturer has released updates for them. If possible, connect them to guest WiFi.