AstroAI Digital Multimeter | $9 | Amazon
If you want to do any electrical work around your house, you need to have a multimeter in your toolbox. This one’s only $9 today on Amazon, and boasts a 4.5 star rating from over 2,000 reviews. At that price, there’s no reason not to add it to your tool box. Hell, you should celebrate by adding some USB ports to your power receptacles, if you ask me.
Just please, be careful.