I would go for the TEAM ORION Pro lap counting.
Team Orion’s Pro Lap Counting System
(PRO LCS) is the ultimate tool for monitoring lap times and ensuring that you are on pace when it comes to vehicle set-ups, varying track conditions and driving adjustments. Just lay the Pro LCS somewhere around the track and every time your vehicle passes by, an infrared beam emitted by the special transmitter installed in your car will count the lap. Specific audible tones let you know that your lap has registered, if you have beaten your predetermined target lap time, or if you have set your fastest lap up to that point. After the adjustable 1-10 minute run with either a staggered or main event type start is completed, all laps can be reviewed individually with your best lap and average lap indicated.
Also available separately is the Pro LCS Software
and data link to help deliver more from your Pro LCS. The PC-Link and software allows you to save, log, and graph your lap times on your Windows® laptop just like full-scale racing teams have done for years.