Checking sensor connection

Hello, i need a simple way to check the wire connection between Arduino and a flow sensor connected to it, so that i could know once the connection is lost. Is there any simple way to accomplish this task ? Please help.

What flow sensor are you talking about and how is it connected that the connection could be lost?

I have connected a flow sensor using 3 wires (Vcc, Ground, signal), and i need the controller to buzz me if the connection between the sensor and controller lost .( i am making a water meter and it's just to prevent tampering )

Monitor the current flow to the sensor. If it is out of normal range, raise an alarm.

But using a current sensor would so be priced .

ferwed:
But using a current sensor would so be priced .

If you let us know what flow sensor your using then maybe the arduino can do the sensing.

Here is it : http://www.fut-electronics.com/wp-content/plugins/fe_downloads/Uploads/Flow%20rate%20sensor%20with%20arduino.pdf

There is almost no useful information in that PDF file about the sensor itself, but the active element is identified as a Hall effect sensor. In that case, the current draw is likely to be a few mA, and a $0.05 LED (i.e. the input LED of an optocoupler) would suffice to monitor the supply current.

I did NOT get it . can you explain in details

The details will depend on what type of Hall effect device is present in the flow rate sensor. Without that information, I don't think it is useful to provide guesses about which circuit might work. You will have to experiment.

May this would be useful : http://store.fut-electronics.com/POW110D3B.html
But i know that optocoupler is used for circuit isolation, how can we monitor current.

This looks like the datasheet for the sensor.
You could maybe make a circuit to monitor the current draw (datasheet says 15mA max @ 5V), assuming it will be reasonably steady and not dependant on where the paddle stops (you really need a device to check this out though).
The problem will maybe be detecting if the yellow wire is cut/tampered with to prevent pulses getting through.