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Your camera will fire when you touch two of the wires in your remote together. The trick is to figure out how to make a motion sensor do this for you. There are canned options that are sometimes way overpriced, and there are <$50 options that are incredibly capable and customizable, but require some time investment for a non electronics geek. The new Arduino based thingie that was featured in dpreview a few weeks back might be a good option for something that is relatively cheap and won't take a lot of time investment.