CRL's Thru-Glass Two-Way Digital Electronic Communicators contain the latest advancements in electronic sound transmission devices. Standard units fit barriers from 1/4 inches (6 mm) to 4 inches (102 mm) thick, and bullet resistant models are available up to Level 3. Model choices include standard or bullet-resistant 120V AC Plug-In Transformer Models and 12V DC Rechargeable Battery Powered models. The absence of exterior screws or fasteners makes them tamper-resistant. Three headset styles and many other accessories are available from CRL. All units are supplied with mounting hardware and instructions to fit 1/4-inch to 1-inch (6 to 25 mm) thick barrier glass and up to a 4-inch (102mm) barrier when using the extension screw kit. Standard finishes are satin or Black anodized.