The Nearby Glasses app detects and warns users of smart glasses nearby, using Bluetooth Low Energy signals to identify devices from specific manufacturers. The app is free, open-source, and available for Android and iOS, with a simple and heuristic approach to detection. The app's author emphasizes the potential risks of smart glasses, including covert surveillance and facial recognition, and encourages users to proceed with caution. The app is not foolproof and may produce false positives, but it can be a useful tool for those concerned about privacy.