Abstract: An example adapter device includes a host-side connector to connect to a host device, the host-side connector including a host-side electrical contact to connect to a corresponding electrical contact of the host device. The adapter device further includes a storage-side connector to connect to storage devices operable under different protocols, the storage-side connector including a storage-side electrical contact to connect to a connected storage device. The adapter device further includes a circuit to apply a bias voltage to the host-side electrical contact. The host-side electrical contact is to provide a protocol-indicating voltage to indicate to the host device a protocol of the connected storage device. The protocol-indicating voltage is dependent on the connected storage device's influence on the bias voltage.