An apparatus for use in a wellbore, comprising: a tool string, a plurality of sensors including at least a first sensor to detect pressure signals including a first sequence of pressure pulses in an inner conduit of the tool string, and at least a second sensor to detect pressure signals including a second sequence of pressure pulses in an annulus outside the tool string; and characterised by a controller configured to actuate a tool (22, 23, 14) in the tool string in response to a logical combination of outputs from the sensors (100, 102), wherein the outputs of the sensors (100, 102) are responsive to the respective pressure signals, wherein the controller is configured to actuate the tool (22, 23, 14) in response to the logical combination of the outputs by: determining whether the pressure signals received by one of the first and second sensors (100, 102) match a predefined signature; in response to determining that the pressure signals received by the one of the first and second sensors (100, 102) match the predefined signature, determining whether the pressure signals received by another one of the first and second sensors (100, 102) satisfy a predetermined condition; and actuating the tool (22, 23, 14) in response to the pressure signals received by the one of the first and second sensors (100, 102) matching the predefined signature and the pressure signals received by the other one of the first and second sensors (100, 102) satisfying the predetermined condition. a tool string, a plurality of sensors including at least a first sensor to detect pressure signals including a first sequence of pressure pulses in an inner conduit of the tool string, and at least a second sensor to detect pressure signals including a second sequence of pressure pulses in an annulus outside the tool string; and characterised by a controller configured to actuate a tool (22, 23, 14) in the tool string in response to a logical combination of outputs from the sensors (100, 102), wherein the outputs of the sensors (100, 102) are responsive to the respective pressure signals, wherein the controller is configured to actuate the tool (22, 23, 14) in response to the logical combination of the outputs by: determining whether the pressure signals received by one of the first and second sensors (100, 102) match a predefined signature; in response to determining that the pressure signals received by the one of the first and second sensors (100, 102) match the predefined signature, determining whether the pressure signals received by another one of the first and second sensors (100, 102) satisfy a predetermined condition; and actuating the tool (22, 23, 14) in response to the pressure signals received by the one of the first and second sensors (100, 102) matching the predefined signature and the pressure signals received by the other one of the first and second sensors (100, 102) satisfying the predetermined condition. determining whether the pressure signals received by one of the first and second sensors (100, 102) match a predefined signature; in response to determining that the pressure signals received by the one of the first and second sensors (100, 102) match the predefined signature, determining whether the pressure signals received by another one of the first and second sensors (100, 102) satisfy a predetermined condition; and actuating the tool (22, 23, 14) in response to the pressure signals received by the one of the first and second sensors (100, 102) matching the predefined signature and the pressure signals received by the other one of the first and second sensors (100, 102) satisfying the predetermined condition.