Maybe you should contact the Johnson County Director of Emergency Management and Homeland Security Mike Selves. He is a pretty cool person when it comes to talking about the sirens. BTW here is their testing schedule straight from the website:
http://www.jocoem.org/outdoor_warning.htm
Testing
The outdoor warning system for Johnson County is tested at 11:00am on the first Wednesday of the month from February through November. No tests are conducted in December or January, or any other scheduled test date when extreme cold and/or heavy icing might damage the equipment. Tests are also cancelled whenever there is severe weather (or potential severe weather) occurring in the local area and activating the outdoor warning system might cause confusion as to whether the activation is real event.
In March siren activation is done as part of a statewide tornado drill in conjunction with Severe Weather Awareness Week. These drills are typically conducted on Tuesday or Thursday (back-up date) afternoon, late enough as not to disrupt the school lunch period.