Replacing a cracked iPhone screen isn't as simple as swapping out a piece of glass and turning a few tiny screws. At least not according to Apple, which has built a custom machine to repair cracked and shattered iPhone screens.

The company is deploying 400 of these machines to authorized retailers in 25 countries by the end of the year, according to Apple (AAPL). They will be able to do same-day screen repairs.

The machines do more than just replace the glass. They put the phone through a mini-factory process, optimizing the display for each individual device, says Apple. The glass is connected to a number of sensors and, if not replaced correctly, could lead to dead spots on the screen, a broken fingerprint sensor or home button and unsightly raised edges.

Apple says it has had the devices, called Horizon Machines, for a few years. Some authorized stores in the Bay Area, London and a few other locations have been using them as part of a pilot program. This is the first major roll out for the technology, and one Apple hopes will reduce the number of people queued up at its Genius Bars.

Related: It will now cost just $29 to fix a cracked iPhone

Typically, authorized Apple stores need to send a phone away to an Apple service facility to be repaired, which could take days. But not everyone lives near an Apple store, so independent stores and sites have popped up around the world to meet the demand for quick and cheap phone screen repairs.

Apple has lowered the price for a replacement to $129 for newer devices, and $29 if you have Apple Care. But for people without Apple Care, that little kiosk in the middle of a mall can be a better deal. Authorized third-party service providers can set their own prices for repairs using the machine.

Having a non-Apple technician swap out your screen no longer automatically voids the iPhone's warranty. However, if it has resulted in deeper problems inside the device, Apple repair might charge more to fix it.

Like other hardware companies, Apple has tried to keep tight control over repairs for its products. Users are discouraged from attempting any repairs themselves, even something as simple as installing a new battery. Any unofficial tinkering can void warranties, violate end license user agreements, even break the law.

The roll out was first reported by Reuters, which got a sneak peak of the machine. It says they're the size of a microwave and use a mechanical finger to repeatedly poke the screen in order to test its sensitivity.