Nowadays, riding a bicycle is a very common activity performed by many people, either to do sport or as a way of transport. The main problem of this activity is the high probability to have an accident. This is due to the fact that motor vehicles and bicycles share the same roads. Unfortunately, the increase in the number of cyclists has also raised the level of accidents caused by car drivers. One of the reasons is the breach of the law that binds drivers to respect a minimum distance of 1,5 m when overtaking a bicycle. The purpose of this project is to equip cyclists with a simple and affordable system which would allow them report any danger situation caused by drivers. In addition, this system would send an automatic alert message in case of accident. The first part of this security system consists of a distance sensor connected to a Raspberry Pi 3 which allows us obtain the distance between the bicycle and the vehicles that overtake it. If this vehicle do not respect the minimum distance, the device will take several photos using a camera connected to the Raspberry Pi and attached to the handlebars. This device is connected to a smartphone through an application particularly developed for this project. In order to detect an eventual accident, it is needed to use some of the smartphone's built-in sensors: accelerometer, gyroscope and GPS. The data provided by these sensors is processed using an algorithm that detects an eventual fall or accident. In case of accident, an alert email, which contains the current cyclist's position, is sent to a pre-defined contact person.