This document explains the implementation and operation of a car key system consisting in an Android application running on a mobile phone which uses Bluetooth Low Energy (BLE) and a peripheral device which works with the Ultra Wide Band (UWB) technology to communicate with a car which also has BLE and UWB devices up and running. The system uses BLE to communicate the mobile with the car and send user instructions to the car making use of the authentication and encryption advantages of the BLE protocol. UWB is very precise and efficient measuring distances wirelessly, in this project this technology is used combined with a trilateration mathematical algorithm to estimate the location of the user respect to the car and send this data encrypted through BLE. Combining both BLE and UWB allows to offer a robust security framework, including the encryption and authentication advantages offered by BLE and also avoiding relay attacks by adding the location obtained through UWB to the authentication scheme. Additionally, knowing the location of the mobile is useful for features such as to open only the door of the side in which the user is located without the needing of the user to do any movement or operation.