This GSM spy bug is built into a real functioning office desk top style calculator. The microphone works amazingly well and better than any other gsm spy bugs I have heard. It has no echo and it clearly heard my secretary on the other side of a very large office talking on the phone. This model is the real thing and a perfect listening device with a standard 3 day standby &/or 5 hours of listening. Also available is a long life and ultra life with up to 30 days standby &/or 24 hours of actual usage. It is totally discreet and impossible to know it is a listening device as no external parts are visible. It does require taking the calculator apart to install sim card (not included) this is simple to do and care must be taken when carrying this out. it will turn itself on when sim card is fitted ready to place and call from any phone worldwide. You can call it at anytime from anywhere to listen and monitor sounds up to 7 metres from the calculators location. Also features sound activated call back so that when a sound is heard it calls or texts your dedicated phone to notify you.