In skydiving, an automatic activation device (AAD) is a dead man's switch consisting of an electronic-pyrotechnic or mechanical device that automatically opens the main or reserve parachute container at a preset altitude or after a preset time. AADs are typically used to open the reserve parachute container at a preset altitude if the descent rate exceeds a preset activation speed. This indicates that the user has not opened their parachute, or that the parachute is malfunctioning and is not slowing the descent rate sufficiently. The older style mechanical AADs are falling out of fashion in favour of newer style electronic-pyrotechnic models. These newer models have been proven more reliable as their built-in computers allow for better estimation of altitude and vertical speed. Electronic AADs typically employ a small pyrotechnic charge to sever the reserve container closing loop, allowing the spring-loaded reserve pilot chute to deploy. Examples Examples of specific AADs are: Safety AADs can malfunction and deploy the reserve parachute when the firing parameters have not been met. This will result in either a premature reserve deployment if it happens prior to main deployment, or in both parachutes being deployed if it happens after main deployment. A premature reserve deployment can be dangerous if it happens while exiting the aircraft, in close proximity to other skydivers in freefall, or if the skydiver is falling faster than the safe deployment speed, which can result in catastrophic equipment failure and injury or even death of the jumper. A deployment of both canopies could result in an entanglement between the two canopies. Undesired AAD activations can also occur due to user error. This can happen if the skydiver deploys the main canopy too low, and the AAD activates while the main is deploying, resulting in both parachutes being deployed. It can also happen if the AAD is not calibrated to the correct ground level, either due to turning the AAD on at a location with a different elevation than the airport, or entering an incorrect altitude offset (a feature that is normally used to compensate for a landing zone that is at a different elevation than the airport). Some models of AAD carry a risk of deploying the reserve inside the aircraft in cases of sudden aircraft depressurization, or during a rapid descent when landing with the aircraft. The risk of an AAD malfunction is far smaller than the risk of a situation