I used one of the MicroSizer Lap Counters for tuning purposes before I put down my track and it worked perfectly.I see them on ebay once in a while.
amazon has an outrageous price
I'd sell this one for a third of that price.
1 car only
lap times and more (example 3.21 seconds) and maybe lap count per 3 minute heats.
I bought every one I could find when Toys 'R Us clearanced them out for 25 cents each. I must have sold over 100 on eBay.