I had an Android Phone battery swell and open the phone. I tried to repair it. Ordered the wrong replacement battery. Had to wait months for the correct battery. It was fixed and "mostly" works.
I built a current sensor torrid to determine when the hot water recirculating pump was on. Sent a signal via cheap remote controls to an LED
Then added a temperature sensor to see what the temp was at the water faucet. Temp was sent Arduino to Arduino via Bluetooth.
I dug out a giant Burrows (B7971) Nixie tube I had for years. It did not operate to spec. (It took >450 volts to light, should have been 180.)
Bought a "new old stock tube" on line. It had a hole in it. got a refund. Bought another tube and built a "Flashy thing" using an Arduino. (MS Office pix editor does strange things when you rotate a pix) This is the letter "D".