The ultimate professional listen through wall system that can hear sound through concrete, metal, wood, brick in fact any solid surface. This serious piece of kit is not for the faint hearted, be warned you can hear through indoor and outdoor walls. Some surfaces work better than others and density / thickness can also restrict its performance. We have received varied results as it depends entirely on the surface you use and many other factors such as distance and volume. Place the Sonde contact microphone to the surface of interest and listen it has variable gain and volume settings. You may need to experiment further with the position for better results and we can not guarantee results first time every time. We guarantee it will hear audible sound through any door or single brick / cavity walls. Anything else is not guaranteed and returns for using this beyond it's means is not accepted. Unless it is faulty not hearing through doors, windows, internal walls etc. Another serious matter is the headphones used, included is good quality earbuds but if you use noise cancelling headphones costing £50-£200 this improves the sound hugely. F-999B professional listen through wall spy ear is a highly sensitive contact and probe microphone amplifier system. Both microphone and amplifier are built into a strong metal housings for durability. Enhanced quality sound and performance capable of listening to conversations in adjoining rooms and houses. High quality earbuds a built in lithium battery and all accessories needed to achieve the job. The highest sensitive contact microphone available with superior detection ability using best quartz crystal piezo. This quality component is more sensitive and clearer than anything else out there and if this does not work then nothing will for less than £100. Package includes: Sonde contact microphone Probe / Needle microphone Microphone / Headphone Amplifier 2.5mm-3.5mm stereo record lead Charger and Metal case