Reply to post: "not the sort of thing one can sneak into a room easily"

"not the sort of thing one can sneak into a room easily"

https://www.amazon.co.uk/20Vrms-Ultrasonic-Transducer-Sensor-Detector/dp/B00P0BD6PA

https://www.amazon.co.uk/MakerHawk-NodeMcu-Development-ESP8266-ESP-12F/dp/B071S8MWTY

https://www.amazon.co.uk/Value-Charger-Adapter-Quadcopter-XC317/dp/B01F6YUGLW

https://www.amazon.co.uk/XCSOURCE-Battery-Lithium-Charging-TE668/dp/B01N2Z24VL

I'm sure this would be difficult to sneak into a room. It must be all the size of a moderately voluminous matchbox.