Laser timers for sprints
A laser sprint timer is a timing gate that uses a laser and a reflector. Kits on Amazon start around $150 for one gate and run to about $450 for three. They time a 40 well enough if you set them up with care.
How a laser timer works
Each gate is a laser on a stand pointed at a reflector across the lane. As long as the beam bounces back, nothing happens. When your body cuts it, the unit stamps the time and sends it to a display or the other gate. A one-gate kit times laps or a flying run through a single line. For a 40 from a standing start, you need two gates, and for a 10-yard split on top of that, three.
What they cost
Unbranded laser kits on Amazon, sold under names like YZ and TimeRider, list at about $149 for a single gate and $399 to $449 for two or three. Branded laser systems cost more: Dashr Blue, a laser and reflector system, starts at $690 for two gates. Amazon prices move often, so check the listing.
Setup tips
Each laser has to be lined up with its reflector. Point it, check the unit shows a solid beam, then walk through the line once before the first rep.
Set the beam at hip height. At chest height, a swinging arm breaks the beam early far more often, which makes the time look fast. Keep the same start distance behind the first beam every session too, since half a meter more run-up makes a 10 m time several hundredths faster.
What a laser can't tell you
A laser gives you the time between two beams. It doesn't see what happened in between, so a 40 time alone won't tell you whether you lost time out of the stance or faded at the end. For that, you need more gates or a system that tracks you the whole way.
Sprintbrick follows you for the whole run. A receiver behind the start measures the distance to a sensor on your lower back 100 times a second, and the app reports splits at 10, 20, 30 and 40 yards, every 10 m to 100 m, your top speed and where you hit it. You have nothing to align, and the only thing on the ground is the receiver.