This application relates to methods and apparatus for detecting the presence of an accessory device connected to a host device via suitable connector. The apparatus includes a test signal generator and impedance measuring block. The apparatus is operable in an accessory connection discovery mode wherein the test signal generator applies a test signal to a first contact of the connector while a second contact of is connected to a reference node. The impedance measuring determines an impedance measure between said first and second contacts and the apparatus determines whether an accessory is connected based on said measure of impedance. The test signal generator may also have functionality including a microphone bias generator and the impedance measuring block may be a microphone detect block. The contact to which the test signal is applied may be varied while the remaining contact of the connector are connected to the reference node.