Ask HN: Home/Office Monitoring System

We just got a new office; and for security purposes, we'd like to have a bunch of webcams, with data streamed to a centralized server (for motion detection / logging).

"Privacy" is not a problem as it's a small company and all the founders are okay with it.

What are the best open source tools for this? We'd like the backend to be linux, and for the actual cameras, just get a bunch of cheap cameras (that can hopefully stream over wireless or network).