Wireless Communication with XBee Radios - Exploring Arduino: Tools and Techniques for Engineering Wizardry - page 247

Figure 11-19: Wireless doorbell system diagram
TransmitterHardware
First, build the hardware for the doorbell component, which will be referred to
as the transmitter. You need a button with a pull-down resistor, connected to
a digital input on an Arduino with a mounted XBee shield (see Figure 11-20).
Figure 11-20: Wireless doorbell transmitter