There is provided a field device activated by a battery and housed in a pressure-resistant and explosion-proof container. The device includes: an external interface unit comprising: an infrared communication unit configured to communicate with an external infrared communication device through a window attached to the container; and a display unit configured to display status information about the field device; and a power controller configured to determine whether power from the battery should be switched on or off, in response to a request from the external interface unit.