ALTCHA Sentinel is a self-hosted security layer for forms, sign-ups, logins and APIs, built on the ALTCHA captcha technology. It scores the risk of each request and responds proportionally, challenging or blocking suspicious traffic while leaving genuine users alone. According to the documentation, it includes adaptive captcha difficulty, interaction analysis, a self-tuning challenge policy, threat intelligence for IP blocking, spam classification, phishing URL detection and multi-layer rate limiting. Sentinel is installed on the customer's own infrastructure, for example with Docker, Kubernetes or cloud services, and configured with API keys and an embedded client widget. The vendor also describes optional air-gapped operation.
Sentinel is developed by BAU Software s.r.o. in Czechia, which also operates the open-source ALTCHA widget. Unlike the widget, Sentinel is a paid product with its own licence and end-user agreement. Because it runs on infrastructure the organisation controls, the organisation decides where data is processed; the vendor does not host it.