A method and system for controlling bias voltage for use with an electrostatic transducer are provided. The invention reveals a recorder installed in a motor vehicle with a microphone positioned on the driver’s side and a camera system preferably concealed in a decorative ornament. The method for replacing an open-close valve connected to the hydrogen supply-release pipe includes supplying inert gas through a gas supply pipe to the tank body and replacing the open-close valve in a state in which inert gas can be released from the hydrogen supply-release pipe. Then, the needles 53 retain the solution including biological samples and form spots of the solution on the substrates 3. A signaling system characterized by reduced designing and manufacturing costs is provided. In this method, beads are prepared with a known ligand specific for a particular type of cell and incubated for 24 to 72 hours with a sample of the body fluid being tested.