tool to measure distance ran?

[stoxtrader]

I just started playing indoor soccer and thought it would be very interesting to track how much I run during a game and also to track it over time, I would assume as I get more fit that I would increase my distance both because I stay on the field longer without substitution and because I am more active when on it.

can anyone suggest a good tool that can track this kind of thing but not affect my play in an indoor soccer game? tx.