If you use the Plug-In Wireless Chime or the Battery-Operated Wireless Chime to receive audible notification when a visitor arrives at your doorstep, you can expand this wireless doorbell system by mounting an Additional Wireless Chime Transmitter at another entry to your home. Just mount this battery-powered doorbell at your front door, and when a visitor presses it, it transmits wirelessly up to 100 feet to the chime receiver in your home. The Wireless Chime kits are sold separately.