Of course this isn't very likely, but it's a question that we get on occasion. The good news is that the techie type people a few years ago figured out a system that works and they created the Automatic Activation Device or more commonly called an AAD.
The AAD is a small computer that constantly measures your altitude and how fast you are falling. Models will differ, but essentially if you are falling fast at a lower altitude this little computer will send a signal to a cutter that will cut the closing loop on your reserve parachute which will in turn allow your reserve parachute to deploy. So essentially what this means is that if your instructor was unable to activate your parachute for some reason the AAD will automatically activate your reserve parachute for you. There are currently three manufacturers of AAD's that we utilize and recommend. These manufacturers are Cypres, Vigil and M2. Each of these manufacturers make AADs for both Tandem and Sport Systems. In the spirit of encouraging safe skydiving AADs are mandatory at Skydive Vancouver Island.