A single laser fired through a keyhole can expose everything inside a room
&quot;Seeing through walls&quot; motion detection can be done with Doppler imaging and commodity Wi-Fi today using custom firmware.  Hundreds of research papers have been published on this topic. The upcoming IEEE 802.11bf standard is scheduled to add that capability to every router in 2024, <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=27123493" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=27123493</a> &amp; <a href="https:&#x2F;&#x2F;www.theregister.com&#x2F;2021&#x2F;03&#x2F;31&#x2F;wifi_devices_monitoring&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.theregister.com&#x2F;2021&#x2F;03&#x2F;31&#x2F;wifi_devices_monitori...</a><p><i>&gt; In three years or so, the Wi-Fi specification is scheduled to get an upgrade that will turn wireless devices into sensors capable of gathering data about the people and objects bathed in their signals... When 802.11bf will be finalized and introduced as an IEEE standard in September 2024, Wi-Fi will cease to be a communication-only standard and will legitimately become a full-fledged sensing paradigm... tracking can be done surreptitiously because Wi-Fi signals can penetrate walls, don&#x27;t require light, and don&#x27;t offer any visible indicator of their presence.</i><p>IEEE 802.11bf paper (March 2021): <a href="https:&#x2F;&#x2F;arxiv.org&#x2F;abs&#x2F;2103.14918" rel="nofollow">https:&#x2F;&#x2F;arxiv.org&#x2F;abs&#x2F;2103.14918</a><p>Theory: <a href="https:&#x2F;&#x2F;groups.csail.mit.edu&#x2F;netmit&#x2F;sFFT&#x2F;soda_paper.pdf" rel="nofollow">https:&#x2F;&#x2F;groups.csail.mit.edu&#x2F;netmit&#x2F;sFFT&#x2F;soda_paper.pdf</a>