Power on mobile phone detector circuit

Circuit working principle: This circuit can detect any
transmission signal of calls, short messages and videos , even if the mobile phone is in silent mode. Once the circuit detects the radio frequency transmission signal
from the powered-on mobile phone , it will immediately sound an alarm and drive the LED to flash. The frequency band used by mobile phones is 0.9-3 GHz and the wavelength is 3.3-10 cm, so the detector circuit designed in this article should have the ability to detect the gigahertz frequency band.