The Ubiquitous Pi Garage Door Opener but with a Tkinter Front End and an Arduino monitoring if the Doors are open too long via the common HC – SR04 Ultrasonic modules.
Pi and Arduino 
Ultrasonic Detector 
Tkinter Front End
A basement Water Leak Detector using standard Arduino Water Level Sensor with a NodeMCU monitor able to provide phone notifications utilizing IFTTT.
Sensor next to water heater 
Arduino Sensor 
NodeMCU Monitor
An Electronic Pitot Tube able to provide notifications in case of Fan Failure.
Mech & Elec Pitot Tubes 
NodeMCU Monitor