1. A method for detecting sensor placement, comprising: receiving a signal corresponding to absorption of at least one wavelength of light by a patient's tissue; generating a plethysmographic waveform from the signal; determining an identifying characteristic of the plethysmographic waveform using a processor; and determining a physical location of the sensor on the patient's body based on a comparison of the identifying characteristic with defined critera associated with different physical locations on the patient's body using the processor.