Effective against any microphone based eavesdropping device including RF transmitters (bugs), hard-wired microphones (including contact type) and shotgun microphones. It also protects against microwave or laser reflection types of eavesdropping devices which monitor the sound waves reflecting off of glass surfaces such as windows. The sound from the jammer constantly varies in frequency and amplitude. All the eavesdropper will hear is a loud hissing noise. The convenient push button control lets you select the level of protection for each situation. One unit will protect up to 200 sq. ft. For protecting rooms larger than this, we recommend an additional jammer for each 200 sq. ft. of area. The AJ-40 is powered by one rechargeable 9 volt Lithium Ion battery (battery and charger included). The battery should operate the unit for 3-6 hours of continuous use depending on the volume level selected. Recharge time should be under 2 hours.