The IMSI Catcher!

Guys, how do you think government agents or P.I`s spy on someone who is termed as a threat??One way is through the IMSI Catcher that taps the guys phone. Hear is a short story about the device:

THE IMSI CATCHER:

An International Mobile Subscriber Identity-catcher, or IMSI-catcher, is a telephone eavesdropping device used for intercepting mobile phone traffic and tracking location data of mobile phone users. Essentially a dummy mobile tower acting between the target mobile phone and the service provider's real towers, it is considered a man-in-the-middle attack. The 3G wireless standard mitigates some risk due to mutual authentication required from both the handset and the network. However, sophisticated attacks may be able to downgrade 3G and LTE to non-LTE network services which do not require mutual authentication.
IMSI-catchers are used in the United States and other countries by law enforcement and intelligence agencies, but their use has raised significant civil liberty and privacy concerns and is strictly regulated in some countries such as Germany. Some countries do not even have encrypted phone data traffic (or very weak encryption), thus rendering an IMSI-catcher unnecessary.

HOW IT WORKS:

Every mobile phone has the requirement to optimize the reception. If there is more than one base station of the subscribed network operator accessible, it will always choose the one with the strongest signal. An IMSI-catcher masquerades as a base station and causes every mobile phone of the simulated network operator within a defined radius to log in. With the help of a special identity request, it is able to force the transmission of the IMSI.
The IMSI-catcher subjects the phones in its vicinity to a man-in-the-middle attack, acting to them as a preferred base station in terms of signal strength. With the help of a SIM, it simultaneously logs into the GSM network as a mobile station. Since the encryption mode is chosen by the base station, the IMSI-catcher can induce the mobile station to use no encryption at all. Hence it can encrypt the plain text traffic from the mobile station and pass it to the base station.

There is only an indirect connection from mobile station via IMSI-catcher to the GSM network. For this reason, incoming phone calls cannot generally be patched through to the mobile station by the GSM network, although more modern versions of these devices have their own mobile patch-through solutions in order to provide this functionality.

HOW TO DETECT THE IMSI CATCHER:
Some preliminary research has been done in trying to detect and frustrate IMSI-catchers. One such project is through the Osmocom open source mobile station software. This is a special type of mobile phone firmware that can be used to detect and fingerprint certain network characteristics of IMSI-catchers, and warn the user that there is such a device operating in their area. But this firmware/software-based detection is strongly limited to a select few, outdated GSM mobile phones (i.e. Motorola) that are no longer available on the open market. The main problem is the closed-source nature of the major mobile phone producers.
The application Android IMSI-Catcher Detector (AIMSICD) is being developed to detect and circumvent IMSI-catchers.:

You wanna try it just cost 1400 dollars:the simplest and easiest IMSI Catcher you will get in the market.!