# Sentinels Sentinels are similar to Validators, except they cannot create blocks nor act on their own. It is required that both randomly selected Validators and Sentinels send the same data to the requester, otherwise they will be reported to the network as a malicious node. AppLayer Labs and its partners host them to ensure that will not happen. Sentinels are open for trusted 3rd parties to host and are KYC'd entities with a high level of scrutiny. Eventually as the network and underlying technology matures, Sentinels will be phased out in favor of a fully permissionless system. Sentinels require 200,000 $APPL tokens as a prerequisite and are only accepted by the network after a whitelisting by AppLayer Labs. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.applayer.com/testnet/how-applayer-works/sentinels.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.