In this work a demonstrator for phone as a key has been developed. This demonstrator estimates the position of a mobile device in and around a test vehicle. Trilateration, ROCRSSI and fingerprinting with neural networks have been investigated for the localization of the mobile device. To filter the input data Kalman filter and average mean filter have been investigated. The best performing technique was determined to be the use of neural networks with a Kalman filter. The resulting demonstrator can determine if the mobile device is within the ranges of three predefined zones for the technology and three zones defined in the thesis. The demonstrator can estimate the location of the mobile device in real-time for these zones.