It looks for infrared light. This will only detect a small subset of surveillance cameras that actively use infrared light for illumination. There are tons of dome cameras, and such that don't use infrared light.

It's a cool art project.

There was a research paper I found on detecting hidden cameras that emitted high power IR light, and looked for reflective sources. Potentially, you could listen to EM noise, and then introduce visual noise to the environment. It turns out, this is a hard problem to actually solve.