Rather than WiFi built into the device, why not using something like ZigBee (what the Nest Protect uses to talk between devices) to connect to a small WiFi enab

Rather than WiFi built into the device, why not using something like ZigBee (what the Nest Protect uses to talk between devices) to connect to a small WiFi enabled plug that fits into an electrical outlet? Would this work? If the battery life is still a problem then I wouldn't have a problem with having a detachable module for the Nest that can be removed once a week and manually recharged.