I have recently added the RS 270-1402 34" antenna to my cm15a. All I did was remove the plastic over the antenna, stripped off enough insulation to crimp and eyelet on the wire. Found a screw and nut to fit through the hole of the replacement antenna and clamped the wire to the antenna. With the antenna fully extended and counting the exposed length of the original wire antenna, I have about a full wave antenna and my reception is wonderful. All ds10a sensors on all 5 doors report without a problem and my ms16a on the front porch reaches without a problem. I can even see all my security keychain remotes without any problems.
Here is the antenna I used:
http://www.radioshack.com/product/index.jsp?productId=2062261FYI, the cm15a is located on the main floor in a central location. My house is 2 story with a full basement. Almost 2000 sq feet. Furthest ds10a is about 40 feet line of site. I have another that is about 30' line of site but passes through a few walls, around a few corners and sometimes through a door when closed. Another about 30' away is always behind a second door.
The ms16a is about 25' away and outside on the front porch so it only passes through one outside wall to reach the cm15a.
I did have my cm15a plugged in to the same outlet as my ds7000 but I was getting quirky results. So I moved the ds7000 console to another outlet on the other side of the room and the quirky went away.
Also, I used a palm pad and a kr22a slim remote to trigger a chime and walked throughout the house testing range on both. I could use the palm pad anywhere in the house. The kr22a worked almost every where except in the far corners of the house. This includes the basement for both remotes.