New to Arduino and Need Advice on Project!

Hi,

I'm looking for a variable range - like 2x settings.

-1st setting would make an alarm go off at 4metres
-2nd setting would make an alarm go off at 8metres

Is this possible?

Would be difficult to get the Arduino to recognise the strength of the signal and determine/translate this into distance?! :-?

My Arduino starter kit arrives tomorrow!

Thanks
Ray