Relay Actuator

Software

You can download the Arduino sketch here:
http://code.mios.com/trac/mios_arduino-sensor/browser/trunk/Arduino/RelayActuator

Wire things up

Follow the instructions in ConnectingRadioModule to connect radio module.

Connect the IN1 and IN2 of relay to digital pin 3,4 of Arduino board.
Connect VCC to +5V of the Arduino board. GND to GND.

I used a dual relay module. But the code can easily be adapted to handle more or less relays by modifying RELAY_1 (which digital input first relay is connected to) and NUMBER_OF_RELAYS defines at the top of the sketch code.

Hardware - Purchase guide

To build this sensor you'll need one arduino + radio specified in the base kit found here:
http://code.mios.com/trac/mios_arduino-sensor/wiki/WikiStart#Buyingguide
With the following additional parts:

1x Relay module
​http://www.aliexpress.com/item/5V2-CHANNEL-RELAY-MODULE-FOR-ARDUINO-PIC-ARM-DSP-AVR-ELECTRONIC-SCA-1720/933830812.html

TOTAL SENSOR PRICE: $7.6 (arduino + radio) + $3.3 (relay module) = $10.9