motionsensor
I use a PIR sensor (https://www.sparkfun.com/products/8630) with Arduino to detect people's presence. The sensor detects very well the movements directly in front of it, but it is less sensitive to motions that are more slender or that are further away.
How do I increase the sensitivity of such a sensor?
You can attenuate by using thin sheets of polyethylene. Polyethylene is the same material that the PIR lens is made of. It will pass, but attenuate the wavelengths you are interested in. Find something around .015" and begin stacking until you hit your desired range.
Here is a source: http://www.mcmaster.com/#polyethylene-plastic-sheets/=hc4uvj
You could try a Doppler radar sensor such as the ~10GHz motion sensor modules which are available on the surplus market and from China.
As unlicensed and likely unapproved intentional emitters, they are probably of dubious legality to use, if that bothers you. They're probably safe to use (aside from possible interference with other electronics) but caution is called for- some people get sensitive if they think their DNA might get scrambled or their 'nads nuked.
Best Answer
Angle of detection of a PIR sensor is dictated by the shape and construction of its lens. There is no way to modify it in software or in the electronics.
Distance depends on the power of the IR source as well as the sensitivity of the IR sensor. This may be able to be tweaked, but the specifics will depend on the schematic as well as the components in use.