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 criteria associated with different physical locations on the patient's body using the processor, wherein determining the physical location of the sensor comprises determining whether the physical location of the sensor is a location on an extremity of the patient's body or a location other than an extremity of the patient's body.