SentryPeer is a fraud detection tool designed for VoIP environments. It captures information about attempts to make phone calls, specifically tracking the IP addresses and the numbers being dialed. This information helps service providers and network administrators identify potentially fraudulent activity. When a user makes an outbound call, SentryPeer can check the number against a database of known bad actors, which includes data collected from other SentryPeer nodes. If a match is found, it triggers notifications to warn about possible fraud attempts. The system addresses several common fraud scenarios, including voicemail hacking and phishing attacks. For instance, if an attacker leaves a voicemail and later guesses a user’s PIN, they could dial back using the caller ID. SentryPeer can alert the user to this risk. The project emphasizes user ownership of data, allowing users to choose whether to keep their collected data private or share it with the SentryPeer community through peer-to-peer methods. SentryPeer operates using various technologies, including Docker for easy deployment and OpenDHT for peer-to-peer data sharing. It supports multiple transport methods (UDP, TCP, TLS) and offers a range of APIs for querying data related to bad actors. The tool is open source, promoting transparency and community contributions. Users can run SentryPeer in different modes, either as a honeypot or simply as a data-sharing node, depending on their needs. Installation is straightforward, with commands provided for running the software in a Docker container.