We are very lucky that most cars today come standard with keyless entry, so you can unlock your doors using a remote key fob. The convenience of a remote key fob cannot be overstated, but your car's key fob may not be well-designed. Some are big and bulky, while others have protruding buttons that are easy to press on accident when the keys are in your pocket. If you've ever unintentionally set off your car alarm, you know what I mean. YouTuber Hack 'n' Tink has a Mazda with a key fob that has both problems. For his own sanity, he hacked his key fob remote to make it much smaller.
There are universal remotes on the market, but they are often difficult or impossible to pair to modern cars. Early keyless entry system were vulnerable to hacks, such as replay attacks where a hacker records the wireless signal and then retransmits it when they want to gain entry. To protect against those attacks, manufacturers today use revolving codes that change each time you unlock the car. That means that you can probably only use an official remote from the manufacturer. That was the case with this 2019 Mazda 3 hatchback. Mazda's older key fobs were better, but the current models are big and have buttons that are too easy to inadvertently press.
Both problems were solved here. The new key fob is very small and the buttons are recessed. Hack 'n' Tink started by disassembling his genuine key fob to remove the PCB. That PCB only has a handful of components and most of them sit close together in one small area. He was able to trim off the excess portions of the PCB and relocate the buttons to be closer to the main chip. He then designed a new case in Autodesk Fusion 360 and 3D-printed it to house the trimmed PCB. The new key fob is a mere 19 percent of the volume of the original and it works just as well. Mazda should have made the key fob smaller from the factory, but this project proves that Mazda owners can compensate for that oversight if they have some hacking skills.