I can't find the safety key for my Weslo Cadence G40, is there any way I can get it to work?

You will have to purchase a new key unfortunately. First, go to
www.iconservice.com in the replacement parts link. There you can type your model number/model name found on your machine usually on the bottom of bikes and ellipticals, and underneath the belt when the machine is in spacesaver position on treadmills. It will give you a PDF version that you can download for free. You can also call for a hardcopy but it will cost around $20 with tax and shipping. The number is 1-800-999-3756.

A magnet will make it work.