Carshepherd: An Android RTL-SDR App For the Early Awareness of Nearby Emergency-Service Vehicles

Thank you to Cees for writing in and sharing his Android app, "Carshepherd," which is currently in the pre-release stage. Carshepherd works with a connected RTL-SDR and TETRA antenna to give drivers early awareness of nearby emergency-service activity (such as police, ambulance, fire) by detecting the TETRA uplink signal.

Cees notes that this is essentially the same as what hardware devices like 'Target Blu Eye' do to detect emergency services. Laser/radar detectors are illegal in most European countries, and while not advertised as such for legal reasons, Carshepherd could be a legal alternative for detecting laser/radar speed traps, detecting ProViDa video-based pacing vehicles, or just for general awareness.

The app works by continuously sweeping the TETRA bands, looking for the signature of a TETRA carrier. Once it detects a confirmed uplink carrier, it estimates proximity, which then triggers a readout and audible alert. The TETRA uplink is not always active, but emergency service vehicles often send bursts of uplink data every few seconds with GPS position updates, and, of course, during voice PTT.

The algorithm is based on a large labeled dataset from dozens of real-world test drives. The dataset trains an AI classifier that can even tell you whether an emergency unit is keeping pace with you (e.g., traveling down the same stretch of motorway as you) or whether you are approaching a stationary unit.

Carshepherd currently only works in countries whose emergency services use the TETRA communications protocol, which includes most of Europe and various other countries, but notably not the USA. However, Cees notes that they are working on a US version that will listen to the P25 network.

While Carshepherd has not yet been released, the pricing is indicated as €3.99 per month. You can sign up for the waitlist at www.carshepherd.nl.