Photo Finish

For Single Session Mode, you just need your Android Smartphone. In Multi-Session Mode, all connected phones need an internet connection for the transmission of times. Since wifi is mostly not available at the track, you likely need mobile data. If you only have one SIM card, you can also create a mobile hotspot with one of your phones and join with the other phones. Note that this is not recommended because of the limited range of wifi. Photo Finish needs almost no data (way less than 1 Mb per training session), therefore a small volume flat rate or even prepaid is completely sufficient.

Extremely accurate: With precise alignment of the phones, the expected error is 0.01 seconds or less. This makes Photo Finish more precise than an expensive light barrier system. This is because Photo Finish uses image recognition to determine the chest position of the athlete. A light barrier can also be erroneously triggered by the hand or knee.

You can set up the devices as far apart from each other as you like! This is the case because the transmission of the times happens over the internet. Note that the phones have to be close to each other (within 5 meters) during the connection process.

With good lighting conditions and precise phone alignment, Photo Finish gets a really high accuracy. You can convince yourself of the accuracy with a simple test: Place two smartphones connected in multi-session mode opposite to each other on the same target line and align them exactly vertically and to the respective other camera lens. Then run across the finish line a few times. If the alignment is precise, both smartphones capture the runner at the same time. Typically the times differ by only 0.01 seconds or less.