I'm working on a small fun project that involves setting up multiple wireless alarm systems. Basically, I want to have approximately 10 or more alarms/sensors (not sure whether this will be motion sensitive, small switch, infrared etc...) that will send a WIRELESS signal to an arduino when one or more of them gets tripped. The data transmitted will either be a logical 1 or 0 (alarm triggered or not). The arduino will then communicate with a computer and send an email out notifying me of which sensor tripped. The range will not be more than 50m at most.
My main confusion lies with how to have an arduino listening for multiple wireless sources and keeping track of which source it came from. (Wi-Fi is not an option due to highly unreliable network in my area). I'm hoping to keep the costs down as well since I don't have too much money to spend right now. Any suggestions?