what kind of sensor?

You do not need an a/f guage. The only time that is required is when being dyno tuned and they will have one at the dyno shop. Don't waste your money. Get a different guage instead.

What are your current mods?
 
I think it's very usefull to know if the air/fuel mixture is ok or not,here's my mod so far
PI intake+PI cams
dragon throttle body(75mm)+plenum
U/D pulleys
timing pulley
180 thermostat
screaming demon coils
O/R pro chamber+super turbo mufflers
AND(thats why i want my gauge) a c&l CAI+MAF

I read that some of you did install this kit(c&l) and as a result, the car was on the lean side,so i want to be sure the car will run just right with the right mixture.