You’ll find various stuff around the forum. I like the hardware hack too. I sometimes label my posts with [Hack], but that’s often about modding the device itself or building one device from the components of another.
Many like the ESP8266 boards. I’m more of a Zigbee guy. You should also check out @ogiewon ‘s HubDuino
Not sure if you’re looking for ideas or devices to use. Just about any contact sensor will produce a simple input. I’ve used Insteon in the past, Xiaomi Mijia (easier to take apart and reassemble than Aqara), and Ring alarm Z-Wave contact sensors. An easy mod to appliances is adding a 110v relay to create dry contacts to trigger a contact sensor that has wires soldered to either side of its reed switch.
I typically convert these wired in devices to a power adapter so I never have to buy batteries for them again. I use these buck converters with a 5v USB supply.
Solder, shrink tube, a heat gun and patience are the best tools for the job.