Collective bargaining. Written By: Collective bargaining, the ongoing process of negotiation between representatives of workers and employers to establish the conditions of employment. The collectively determined agreement may cover not only wages but hiring practices, layoffs, promotions, job functions, working conditions and hours, worker discipline and termination, and benefit programs.
Three Parts:Building the Siren's Spinning CylinderBuilding the Siren's Outer PortionFinishing the SirenCommunity Q&A. The distinct rising and falling sound of an air raid siren is produced by a relatively simple machine. While the flatter pitch of most modern emergency vehicle sirens requires electronic circuitry to reproduce, the mechanical siren can be made with basic carpentry tools.
1 Testing sirens, Swiss Federal Office for Civil Protection (page visited on 7 September 2013). 2  The dials atop the siren are connected, via reduction gears, to the perforated disks (in the cylinder beneath the dials) which produce the siren's sound. The dials allow the siren's frequency to be determined.