ATMs are literal money machines, but we doubt you've ever thought about how you might make some cash off them.
Paul Alex, who is now based in Miami, has done exactly that - and he's been sharing all of his secrets on Instagram.
First up, a bit of his backstory - Alex became a police officer at 26, eventually making his way up to a detective at age 28, making over $200k a year.
Hardly a salary to be sneezed at, but Alex wrote on Instagram he was having "3 hours of sleep daily, [and] gave everything to my job."
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So he decided to make a change, and when he was 29 he "started an ATM business hoping to quit my job one day".
This was 2018 - he started buying the machines and grafting to work out where they might be best placed to make the most money, scouting out locations like barber shops and liquor stores. He negotiated with the owners to get them to agree to have his ATMs in their locations, and also had to manually fill them with cash.
In the first month, Alex said he had one ATM and was making $500 a month - by month 18, he had 30 ATMs and was making $15k a month.
Now 35, Alex says he's a millionaire and has seven income streams - along with the ATMs, he also owns a credit card machine business, a Bitcoin ATM business and dabbles in real estate.
According to Alex, getting into the ATM business ultimately let him quit his job, make $20 million, retire his parents and buy a $2.9m house.
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Pretty good going, right?
Plus, there seems to be more than a few other perks to being a millionaire in your 30s - Alex talks a lot about smart investing and how to make side hustles work for you on Instagram, while also showing off some of his flashy purchases, like a Porsche.
But don't go calling Alex an overnight success.
"My overnight success took me 9 years," he wrote on Instagram.
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"It all came down to working hard, saving up my money, and building businesses while working my 9-5 until my side hustle exceeded my 9-5 income."