just found this on wgc, prolly not what your looking for but i thought it was interesting...
Hero Arms 1000rds Electrial AEG Magazine for Marui M14 ( Sound Control )
- Sound Activated Winding
- Powered by 4x AAA Batteries ( Not Included )
- 3 Modes ( Constant Winding for first lading / Off / Sound Control )
- Suitable for Marui M14
Not suitable for AEGs with ROF over 30.
Sound Sensor is more sensitive with gearbox noise generated by upgraded AEGs.
Hero Arms Electric AEG Magazine - M14 Series