Each PocketLab kit contains 5 sensors that measure almost anything, including motion, altitude, light, magnetic fields, etc. The sensors connect wirelessly using Bluetooth on most devices made since 2013. It is recommended to reserve this in advance to ensure that needed apps and extensions can be downloaded. Directions are provided. The replacement fee for each missing PocketLab is $100. Apple Store App: https://apps.apple.com/us/app/the-pocketlab/id1005909631 Google Play Store App: https://play.google.com/store/apps/details?id=com.pocketlab.android&hl=en_US&gl=US Chromebook Extension: https://chrome.google.com/webstore/detail/pocketlab/hcgfdfgomnfebpnlkohhflcdhkllepdk?hl=en .