Motion sensor network


I'm planning to develop a motion sensor system to monitor movement around designated area. It should be mobile enought so that I could plant sensors wherever I am at the moment. Designed primarly for military-style trainings.
I was thinking that if I could plant 5-6+ IR motion sensors around the camp, for example, to detect movement and notify the one whoever is on post.

I was planning to desing a simple receiving system with arduino but what would be the best way to transmit that movement data wirelessly from sensors? Looks like wifi would be the best choice since the sensors should be planted about 30m from the camp and should cover the whole 360 degrees. What modules are easiest to use and set-up? Xbee modules are quite expensive considering I need at least 5 of them plus there are so many different models and It's quite hard for a beginner to figure out which one I need.

Any ideas are appreciated...

Looks like wifi would be the best choice since the sensors should be planted about 30m from the camp and should cover the whole 360 degrees.

No way,
you should use wires to do the communication as the wireless communications will be a beacon to your position....

Well yes you've got a point but wires ain't gonna do. This needs to be wireless.
Next development step could be something like: activating wifi transmitter module only when movement is detected... that way there won't be any beacon to give out position.

check these

low baud rate (4800) but as it only needs to send an node ID + detector ID (2 bytes) when something is detected that is not a problem. 500 feet optimal => 100 feet (30 mtrs) should be feasible.

Idea: the nodes should also warn for low battery.
Idea: an LDR could detect people approaching with a flash lights

I'll look into these. But I was thinking maybe I should get the motion sensor reading value as well instead of just info that it detected something. In the woods for an example, sometime trees just move a little bit because of wind or smth. I need to set a threshold so I wouldn't get an alarm every time a leave drops.

Do the above mentioned modules work in a network as well? When they're all on the same frequency. How can I conf them to send the node ID. Do I need some sort of chip there? Or would it be enough to just send a packet when sensor outputs a reading?

PIR's I know only give a YES/NO signal.
If you have an analog PIR you could use a threshold..

WIth a YES/NO you could add up the amount or duration of signals per second.
If above threshold => action but I expect that it will become unreliable.

The main question is:
How many false positives are you willing to accept for one false negative (intruder)?

how difficult it is to set up this RF link? Only buying a transmitter and receiver and connecting won't do it I persume.
Transmitter has DATA-IN pin. Can I just send sensor module output to this pin and it will transmit this info over 434MHZ for receiver to pick it up? And how can I transmit NODE ID along with the sensor signal to know which one detected movement?