A signal generator includes a main body supported by a holder, an antenna mounted on the main body for emitting electromagnetic waves, a bubble level mounted on the main body for indicating whether the main body is horizontally placed, and two laser generators mounted on the main body for generating laser beams. A trench is patterned in a polyimide layer over a guard ring having a top metal layer. When chewed, the gum may change it’s color in response to the oral fluids or salivary pH level. The control unit is mounted to the rotatable handle.