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This very simple circuit uses the Holtek HT12E encoder IC and an old RF-Tx module I salvaged out of a dead piece of equipment. A list of RF-Tx module manufacturers can be found at the bottom of this page.

Upon receiving a brief input pulse at the "TX" pin that drops from a high level to low, the HT12E initiates an encoded transmission. The encoding is defined by the states of the "address" and "data" inputs of the HT12E. Set the input switches either open or closed to change the encoding. The "address" and "data" inputs of the receiving decoder should match the setting of the HT12E encoder in order for the signal to be considered "valid".

The output of "U2A" in the "basic motion sensor" schematic which drops from "HI" to "LOW" when motion is sensed will work to trigger the HT12E.

I'm still working on drawing up the receiver portion - so check back for updates.

A note concerning antennae:

Antenna choice and layout is VERY IMPORTANT for achieving good results with any of these modules. You might get lucky with just using the loop trace (if included) or a hand-made wire antenna, but for the most reliable operation *BUY* good 1/4 wave whips for Tx and Rx (try different styles for each brand - even different styles on Rx and Tx - see Linx). **Use a ground plane!!** at least on the Tx!!! Fiddle around with size, shape and material for the ground plane until you get good results. I have had very good results using copper foil sheet from a stained glass supplier. If the Tx has a "loop trace" antenna, don't rely on it - it might suffice for short range applications, but if you want maximum range and performance, go with a purchaced 1/4 wave whip. It might even be best to cut the trace feeding the loop before installing the whip antenna.

Some manufacturers of RF Tx / Rx modules:

http://www.rs-components.com (U.K. / worldwide [no US?] - sort of expensive)
??? Nordic VLSI ?????
http://www.quasar.uk.com (UK company - small parts - expensive!)
http://www.rfm.com (small SMT modules).
http://www.rfsolutions.co.uk
http://www.dvp.com
http://www.aeiproducts.com
http://www.ming-micro.com - Inexpensive, basic Tx/Rx - order from Digikey, MPJA, or Rentron.com - I hear it told that these are not that good.
http://www.computronics.com.au/misc/t-r_pair.html (Australia).
http://www.linxtechnologies.com US - info and associated RF parts - FCC pre-approved "drop-in" RF Tx/Rx boards!!.
http://www.radioshack.com On-line sister company to the retail store. Has sold a basic Tx/Rx pair for reasonable price - might still have them.
http://www.lemosint.com/radio.htm - US distributor for Radiometrix, a UK company. A bit expensive for basic Tx/Rx.
http://www.rentron.com/PicBasic/RemoteControl.htm - US. - Sells Ming parts as well as the same modules that www.radioshack.com has and for less $$ (Wen Shing modules). Holtec IC's too.
http://www.laipac.com - Ontario, Canada. Sells Holtek IC's and Wen Shing 433MHz Tx/Rx among other more advanced RF stuff.
Wen Shing - These are the modules that radioshack.com, laipac.com and Rentron sell.

Also check out the various "electronics kits" companies (Glolab, DIY etc.). Most sell some sort of basic RF Tx/Rx (usually with components from one of the above companies). Linx sells antenna and has info on design etc. Some of their items available from Digi-key.
If you're convincing enough almost any of the manufacturers listed above will sell you "engineering samples" in single piece or very low quantities. Obviously the retailers will sell to anyone directly.

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