A method and apparatus for detecting the presence of an input object is provided. The apparatus may include one or more capacitive sensor electrodes, a speaker, a microphone, and a processor. The one or more capacitive sensor electrodes may detect a change in capacitance. The processor may cause the speaker to generate a first audio signal. The microphone may receive a first audio signal having the first frequency and a reflected first audio signal. The processor may determine a first phase difference between the first audio signal and the reflected first audio signal. The apparatus may detect the presence of the input object based on the determined first phase difference and the determined change in capacitance.