It's gotten so hard to find Raspberry Pis these days that there is a site that tracks models, vendors, whether or not they're in stock, and prices.
Repository containing useful links for all things Physical Security.
A curated list of awesome guides, tools, and other resources related to the security and compromise of locks, safes, and keys.
A wiki that documents vendors of surveillance, wiretapping, and interception technologies, what their products are capable of, and the countries that buy their gear and what they use it for. Also discusses some of the issues surrounding large-scale communications interception.