Well, The Thing [0] could potentially show up on a probing sweep if you're careful.

Unless you mean, it happened to be actively transmitting during a(n investigative) sweep.

Still, raises some fun concepts. The sort of things where in this current level of technology you'd almost need to supercool a room for a sweep, blast various RF/sound/etc and look for anything that even remotely warms up, to detect (1) whether something detected something worth recording for later as well as (2) something that might be on the right wavelength/etc to trigger a send.

[0] - https://en.wikipedia.org/wiki/The_Thing_(listening_device)

Someone probably walked by or went to plug in an HDMI and noticed the stark contrast of white toilet paper against a black TV shell, it would be difficult not to notice.