simple remote release mechanism

Need to build a simple release mechanism to release a sting when the activator is near or goes by automatically. need to get an idea of components to use or a simple kit that can perform the function. the actual clamp holding the string is not issue the automatic release is.

rumrunner:
Need to build a simple release mechanism to release a sting when the activator is near or goes by automatically. need to get an idea of components to use or a simple kit that can perform the function. the actual clamp holding the string is not issue the automatic release is.

Activator ? How near is "near" and/or "goes by" ? Close enough for physical contact ?