A process control device comprising: an interface configured to communicate with other devices in a process control system, the process control device and the other devices cooperating to control a process, and the process control device operating to send process control signals to the other devices and/or to receive process control signals from the other devices; a primary power source (112, 206), the primary power source (112, 206) configured to provide power to at least one component (106, 204) of the process control device, which component (106, 204), if not powered, would result in disruption to the control of the process; and a terminal configured to electrically couple the process control device to an auxiliary power source (104, 202) such that the auxiliary power source (104, 202) provides sufficient power to the at least one component (106, 204), the process control device characterized in that the auxiliary power source (104, 202) electrically and/or mechanically actuates a locking mechanism of the process control device when the auxiliary power source (104, 202) is connected to the terminal such that the process control device remains operable to control the process in the absence of the primary power source (112, 206), wherein (i) the locking mechanism of the process control device is configured to prevent the primary power source (112, 206) from being removed from the process control device when the auxiliary power source (104, 202) is not connected to the terminal and/or the process control device is not receiving sufficient power from the auxiliary power source (104, 202) and/or (ii) the locking mechanism of the process control device is configured to maintain the connection between the terminal and the auxiliary power source (104, 202) when the primary power source (112, 206) is uncoupled from the process control device. an interface configured to communicate with other devices in a process control system, the process control device and the other devices cooperating to control a process, and the process control device operating to send process control signals to the other devices and/or to receive process control signals from the other devices; a primary power source (112, 206), the primary power source (112, 206) configured to provide power to at least one component (106, 204) of the process control device, which component (106, 204), if not powered, would result in disruption to the control of the process; and a terminal configured to electrically couple the process control device to an auxiliary power source (104, 202) such that the auxiliary power source (104, 202) provides sufficient power to the at least one component (106, 204), the process control device characterized in that the auxiliary power source (104, 202) electrically and/or mechanically actuates a locking mechanism of the process control device when the auxiliary power source (104, 202) is connected to the terminal such that the process control device remains operable to control the process in the absence of the primary power source (112, 206), wherein (i) the locking mechanism of the process control device is configured to prevent the primary power source (112, 206) from being removed from the process control device when the auxiliary power source (104, 202) is not connected to the terminal and/or the process control device is not receiving sufficient power from the auxiliary power source (104, 202) and/or (ii) the locking mechanism of the process control device is configured to maintain the connection between the terminal and the auxiliary power source (104, 202) when the primary power source (112, 206) is uncoupled from the process control device.