Car Headlights On Reminder
More important than environmental issue of energy saving, avoiding car battery failure when you leave the headlamp turned on overnight in the garage is possibly more important for your concern. This is a circuit of automobile lights-on reminder if you turn off the engine but forget to turn off the main lamp, this circuit will give warning when the headlights are on. The warning can either 12V lamp or sonalert (audible alert). A 2N1305 transistor is used as switch to turn on the alarm when the engine is on. This transistor receives the current from the wire that feeds the headlights. The ignition switch is used to turn on or turn off the alarm. The alarm will not active when the ignition is on wich causes the transistor to bias off. Here is the circuit: