Comment by bgbntty2

Remote audio surveillance probably be accomplished on wired headphones with TEMPEST [0]/Van Eck phreaking [1]. Not sure about which has a better range and which would be stealthier - TEMPEST or the Bluetooth attack. The Bluetooth attack just requires a laptop. Not sure if the TEMPEST attack would require a big antenna.

[0] https://en.wikipedia.org/wiki/Tempest_(codename)

[1] https://en.wikipedia.org/wiki/Van_Eck_phreaking