You can modulate an LED at a very high frequency and with the correct receiver send data[1] theoretically you could put a passive receiver into a light fitting (or something as low tech as a high gain microphone), have it record data and then play it back via the LED&#x27;s, someone walking through the building with the correct receiver could then download the data.<p>It&#x27;s a long shot but intelligence services have done strange things (fake rocks, bugging devices in typewriters, setting up cameras over copy machines etc etc)<p>[1] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Li-Fi" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Li-Fi</a>