If you drive a vehicle that’s less than five years old, chances are you have a key fob instead of a traditional two-sided metal car key. Keyless ignitions were first introduced to the mass market by Mercedes-Benz in 1998, and since that time push-to-start ignition systems have become the standard on everything from Hondas to Hyundais.

Also known as prox fobs, proximity fobs give you both keyless access to your vehicle and control over keyless ignitions. Your key fob transmits short-range radio waves to a receiver inside your car, allowing you to unlock, lock, and start your vehicle while leaving your smart key inside your pocket or purse.Some luxury car manufacturers like BMW have designed their key fob systems to also store user-specific settings, such as the location of the drivers’ seat, rear view mirrors, steering wheel, and even the settings on the audio system so different drivers can have their preferences set at a touch of a button.

Each prox fob is programmed to work with a specific vehicle to help deter theft. Unfortunately, these proximity fobs are easy to lose and expensive to replace, with some car remote fob prices hitting $700 or more. These car fobs are pricey thanks in part to the fact that prox fobs contain a lot of advanced technology in a small package.