My radar detector (Valentine V1 Gen2) literally paid for itself the first time it alerted me of a speed trap ahead. I am guessing it has since saved me 10's of thousands of dollars.

House insulation.

I live in Australia where the minimum insulation required by law is a long way below inadequate, and many cheap contractors go below the minimum because it's so hard to prosecute them.

I already had solar and a house battery, so the next obvious step was replacing the insulation. With my already very low electricity bills I cant say that it literally paid for itself (although it would have without the solar and battery), but it has made the house so much more comfortable. On some summer days, the AC would be using 7kW and barely keeping the inside temperature down to 30°C/85°F. Now it uses 3-5kW and the whole house stays comfortable.

Also, finding and patching the massive gaps from the previous "landlord special" house extension made a huge difference to the temperature of that room, and explained how lizards had managed to get inside.

Put 11.6 KW of solar on the roof. I'll hit break even next year. Should have 15-20 years left of use.

Hair clipper. Paid for itself in two uses. It's been years.

About 3 years I bought a mechanic set of ratchets and wrenches and some other tools for changing my own oil and some other auto repairs. All in I spent about $500. In July, I changed my own brakes and rotors and 2 vehicles I own. On that job alone I saved over $1000 dollars. Not to mention all the times I changed my oil. I also changed my spark plugs on one of my cars and found a gasket leak that I also fixed which was probably another $500.

Best investment of my life.

I guess my bike? Have saved loads of money on bus tickets and it's much more reliable too.

Sewing machine pays for itself quite quickly as paying a tailor to repair your clothes is like 1/3 the cost of a brand new sewing machine, so just repair like 3 items of clothing to get your money back.

I got a hot air rework station with a soldering iron many years ago.

The things I've repaired with it are so numerous, I cannot even recount them all, but here are a few:

• an assortment of gaming controllers
• a ghetto blaster from the 1970's
• a few gaming consoles (Xbox 360, PS3 "Fat Lady")
• retro technology (at least two 3Dfx Voodoo's and a rare Abit motherboard)
• a full-metal eBook Reader (Sony PRS-505) that will probably survive an atomic fallout
• a Panasonic broadcasting camera from the 1990's (because it looked cool and I wanted it to work)
• a few LCD monitors

Even though some of that work was just replacing old capacitors, I have saved so much money by buying "broken" stuff and fixing it up. No regrets. Over the years, I paired the station with a hotplate and a solder sucker and now I could probably open up an electronics repair shop. But I mostly do these repairs for fun. Fixing things calms my mind and soothes my soul.

• Smart Lighting - My mum replaced most the lightblub in our house with Philips Hue. Nearly decade on and still using them which as an Autistic, I love that I can tweak the lighting to however I want from an app and compare to regular lightbulbs, it doesn't give me as much sensory nightmare as I find some of the lighting to be really harsh and distracting.
• Noise-cancelling Headphones - Often use it if I'm in sensory overload, walking as I tend to listen to music as well as being on the bus to distract myself which otherwise, I start panicking how full the bus is.
• Desktop DAC & Bookshelf Speakers - Always find changing volume on OS itself to not be perfect as it too low or high for my liking. I can simply tweak the volume knob of my Desktop DAC to get the volume just right. Also great way to listen to music

My motorcycle has paid for itself many times over in terms of the enjoyment I get out of riding it. It's something I can recommend to anyone, and lets you see the world in a way most people never will.

A local NAS for storing all my files, especially if you consider all the value I deprived from Google and Microsoft by not engaging with their cloud bullshit. Even if you don't, I paid like $500 CAD one single time for a 16 TB server hard drive and $300 for a consumer hard drive I'm using as an offline emergency backup. Meanwhile just 2 TB of Google Drive costs $139.99 CAD per year. I wasn't able to find pricing for 16 TB but assuming it scales linearly (like if I had 8 2TB accounts since Google seemingly doesn't offer any higher capacity for individuals), that would be $1,119.92 per year. Even factoring in the hard drive enclosure and the server itself, they've paid for themselves in literally half a year. That's saying nothing of the kind of internet connection I would need to match the read speed of a mechanical hard drive on the local network. I could literally upgrade my entire house to 10 gigabit with the money I saved.

Setting up a fully automated system to download, track and organise … eh … Linux distributions …onto a NAS under the stairs. I used to subscribe to a bunch of services that would … eh … provide access to all sorts of … eh … Linux distributions … for a flat monthly fee, but I realised that I often was only really interested in one or two specific Linux distribution so I really didn’t need to pay for these services.

Now I just download the … eh … Linux distributions that I actually want to install. It also prevents my kids from … eh … endlessly installing different Linux distributions. Not really a productive use of time.

My solar panels have. Literally.

A lot of my work gear is sort of pricey but it keeps me safe and working. Usually pays itself off within a month or two and will last at least a few years.

My tractor has more than paid for itself.

My Nancy pelosi stock bot has done really well