This document discusses open source sensing and whether it is possible to have both privacy and safety. It argues that an open science approach to physical security could be decentralized, voluntary, experimental, collaborative, transparent and respect privacy more than a top-down surveillance approach. An open source sensing community could help determine how to collect public sensing data in a privacy-oriented way that detects dangerous materials but does not track individuals or non-dangerous substances. The document advocates for no secret software and public access to sensing data.