You can you use rf module 433mhz with encoder decoder ic. check this link to make a rf module.
http://embeddedsystem1.blogspot.in/search/label/decoder
In transmitter side replace the switch with your reed switch so that when the reed switch get active it will send a signal to receiver.
In receiver side replace the led with your arduino digital pin so that when you get signal from transmitter it will be detected on arduino digital pin (high,low).