I have two of Honeywell FG1625RFM (http://www.security.honeywell.com/hsc/products/sensor/gl/31133.html) installed. They are quite inconspicuous. In addition, I ordered (and used) FG701 to install detectors. The FG701 allowed me to play around with install locations. You just need to wire up the FG1625 to the Elk, create a “ElkRP test rule,” and have a second person with FG701 walk around to every window in protection zone. You can do the install without FG701 too.