Bluetooth Low Energy and Smartphones for Automatic Door Locks

Bluetooth Low Energy is becoming increasingly popular in mobile applications due to the possibility of using it for proximity data. Proximity can be estimated by measuring the strength of the Bluetooth signal, and actions can then be performed based on a user’s proximity to a certain location or object. One of the most interesting applications of proximity information is automating common tasks; this paper evaluates Bluetooth Low Energy in the context of using smartphones to automatically unlock a door when a user approaches the door. Measurements were performed to determine signal strength reliability, energy consumption and connection latency. The results show that Bluetooth Low Energy is a suitable technology for proximity-based door locks despite the large variance in signal strength. INTRODUCTION Bluetooth Low Energy (BLE) is a relatively new technology, originally released by Nokia in 2006 under the name Wibree. In 2007, the Bluetooth Special Interest Group (SIG) announced that the Wibree Forum would be merged with the Bluetooth SIG and that the Wibree specification would become part of the Bluetooth Core Specification Version 4.0 as what is today known as Bluetooth Low Energy [14]. The low power consumption of the BLE technology and its ability to connect to smartphones makes it especially suitable for low power sensor devices such as heart rate monitors, cycling computers and thermometers [4]. It is also a suitable technology for use in so called Smart Homes as it communicates using radio transmissions in the 2.4 2.485 GHz band [3]. As a result, Bluetooth Low Energy does not suffer from the same drawbacks as other technologies used in the home, e.g. infrared (IR) remote controls which require line of sight to the device that is being controlled. An interesting result of the fact that Bluetooth uses radio waves for transmission is that a signal strength can be calculated. Using the signal strength, it should be possible to estimate the proximity between two Bluetooth devices. The fact that it might be possible forms the basis of this thesis. Motivation The market for applications using Bluetooth Low Energy is constantly growing. The Bluetooth SIG expects that by the year 2018, more than 90 percent of all Bluetooth enabled devices will support Bluetooth Low Energy [11]. As more and more smartphones gain support for Bluetooth Low Energy, the possibilities of using the technology for new types of applications increase. One of the possibilities is using BLE to detect proximity, which can then be used in a number of interesting areas; this paper will investigate one of them, namely automatic door locks. Purpose The aim of this thesis is to evaluate Bluetooth Low Energy as a technology by focusing on its use in door locks that automatically unlock based on the proximity of a smartphone. This will be accomplished by examining different properties of Bluetooth and comparing the results to what can be found in the literature. By implementing an application for a mobile operating system, the thesis also aims to evaluate what possibilities and restrictions exist in using Bluetooth Low Energy on smartphones. Research Questions Four questions have been formulated to aid in the evaluation of Bluetooth Low Energy. The first is a general question pertaining to how suitable of a technology BLE is for automatic door locks, while the remaining three are more concrete questions which act as guidelines. Is Bluetooth Low Energy a suitable technology for proximity-based automatic door locks? Is it possible to prevent the door from unlocking when a person approaches the door from the inside? A security issue may arise if the door unlocks whenever a person approaches the door regardless of where the person is located relative to it. It is not difficult to imagine several scenarios where a person would want to avoid unlocking the door automatically. One such scenario might be that an enraged person is trying to get through the door, in which case unlocking the door may result in direct danger to the person inside. The paper will discuss the possibility of solving this problem using two Bluetooth devices located on either side of the door. Does the implemented solution affect the smartphone’s battery life negatively in a significant way? One of the main features of Bluetooth Low Energy is the low power consumption. As the implemented application is designed to run continuously in the background on a smartphone it is especially important that it has a minimal effect on the battery life. This paper measures the effect on battery life and compares the results to what can be expected based on theoretical data.