As used in this part, “undetectable knife” means any knife or other instrument, with or without a handguard, that satisfies all of the following requirements:

1. (a) It is capable of ready use as a stabbing weapon that may inflict great bodily injury or death.
2. (b) It is commercially manufactured to be used as a weapon.
3. (c) It is not detectable by a metal detector or magnetometer, either handheld or otherwise, which is set at standard calibration.