One of these little things can monitor your AC drain pan for water buildup. You can spend $50 or more on a commercial solution. With just a little $1 sensor and a microcontroller, you can monitor your AC drain pan remotely, and figure out how you want it to alert you. 

I used a Pico W, because it was simple to make it be a little webserver on my wifi, and power it from a cheap usb wall wart. My alert is just a green led that turns red if there's water. The sensor just changes resistance values based on the resistance between those little circuit board traces that run the length of the board. So far, the microcontroller has managed not to cook in the attic for the last two years. It gets to be unbearably hot up there. 

If I was building this again today, I'd probably try to use something even cheaper than a pico w, after all, a complete webserver for just one sensor is a bit overkill. 

Webserver code for the pico is available all over the Internet, or via your favorite super-duper-intelligence. The other bits are just connecting the sensor, reading the values, and alerting. Very simple stuff with a pico and this little three pin sensor. Most 3 pin sensors just have vcc, ground, and the output pin. The output pin just goes to a selected GPIO pin.