cell phone detection

how to detect the cell even though cell in stand by mode

Define standby mode. If the phone is on but not in use the cell phone will keep in regular contact with the cell tower. When phones are on the "ping" the tower every few minutes. This is how police and emergency services use cell phones to find missing and stranded people.

So if you can detect the RF signal transmitted every few minutes you should be able to detect the cell phone.

how to design Rf transmitter and what is range
standby means cell switch off mode

Are you saying the phone is off and cannot receive calls?

yes sir

If the cell is in stanby mode (cannot receive calls) from what you explained, thenit can't send RF nor receive RF signals, which is the most realistic way by which you can detect it. In the case where a phone is not off or in stanby mode, you can detect its presence even with a simple speaker and capacitors or with a more complex circuit involving caps and and op-amp wired as a voltage to current converter.

sir my main aim is to detect the cell phone when it was switch off so please give idea for that one

What is the purpose for your project? We may be able to help you think outside of the box. If you want to detect a turned of cell phone then you need another device attached to it that will allow you to detect the location.

It also depends on how you are trying to detect it. If you are trying to locate it in a static area, i.e. within a room. Or if you are trying to locate it within clothing that someone is walking around with, or if it is in a stack of material that is being moved from one location to another.

sir is the task given by my faculty i am the 3rd year electronic b-tech student
because my interest they give this task
in our college there is no usage of cell phones SO to detect the cell even switch off mode is task given by my respected faculty

i am trying to locate it in a static area, i.e. within a room. in first phase if it is achieved then i am implement it to next two ways as you are suggested thank you sir for your's helping what can i do for you sir

i read this discussion and i have same problem with yalamarti ramojirao,
can i know how the solution is this ???

This information help me on my project and other electronic students.

electronically there is nothing to detect from a switched off cell phone, so unless you plan to man the gates with airport type security check you cant stop people from bringing cell phones in. but you can build a receiver to detect if a cell phone is turned ON at the faculty (you still cant detect if its at airplane mode)

Cell Phones are at the mercy of the manufacturer. They can be manipulated remotely. The only sure methods are complete shielding or battery removal. A small storage device could even be placed on the board to provide some power when the battery is removed, although it's life would be short. The manufacturers and Law Enforcement are not talking about this. I'm sure external inquires would meet a polite "no-comment". RF can be detected but they probably use burst transmission so the detectable periods are quit short so location could be difficult to ascertain.

http://en.wikipedia.org/wiki/Covert_listening_device