These Sound Switches connect to the TSA device (not included) and can be used to measure the speed of sound in air and through solids.Because the TSA device can measure time intervals to 1/100 of a milliseconds it is possible to put the switches a short distance apart in the lab and measure how long time takes to travel that distance.The quality of the sound source is important. A clean fast rising pulse can be best generated by hitting an empty bottle with the plastic handle of a screwdriver.When the sound arrives at the first switch it starts the Fast Timer in the TSA and when it arrives at the second switch it stops the timer. The switches are latched. The Sound Switches enable pupils to quickly and easily measure the speed of sound in air and in solids.The TSA is not included with the Speed of Sound Switches but is available to purchase separately.