Detector device (10) mounts to a drilling rig (12) to sense sound or vibration signalled from downhole. The device (10) has a transmitter (10,20) to transmit data and/or an alert relating to sensed sound and/or vibration associated with deployment and/or positioning of a tool downhole. The device (10) recognises that one or more predetermined events or a pattern of events or one or more particular sound and/or vibration signatures occur(s). Downhole device (36) has a transmitter (38) transmitting a signal indicating a sensed pressure, position or motion change downhole. Communication between the downhole device and the device at the surface to determine depth or distance e.g. time of flight of a signal emitted by one device and the return signal from the other device or from the send and received times of the signal between the two devices based on their respective timers.