Wireless sensors

Good morning, I've just learnt how to use arduino by the starter kit, and now i want to do some think more. I got interested in wireless communication and I was wondering if it's possible for a sensor to comunicate with the arduino board via wireless. For example, a light sensor could tell my if my kitchen lights are on while i'm in my bedroom. I checked the arduino site and i found out that the wireless shield could help me, but I didn't understand one thing. Do I need two arduino boards (one reciving and one transmitting) with one shield each? And if it is, are there any different systems that allow me to use only one board for all the wireless sensor i want to use? Thanks

Some sensors do have wireless built in but most do not. So in most cases yes you need 2 wireless devices. I really like the NRF24L01 2.4 GHz ones (ebay it).

Also to cheapen it up and shrink it down you can make the sensors with a pro mini arduino. And you can talk to more than 1 sensor (with nrf24l01) with one mega or due doing the heavy work.