An RFID pet door, the pet door comprising: an RFID reader to read an RFID tag on a pet; and a lock coupled to said RFID reader to control access through said pet door in response to an RFID signal from said tag; wherein said RFID reader has two modes, a first operational mode and a second, reduced power mode, and wherein said pet door further comprises: a pet proximity detector coupled to said RFID reader to detect when a pet is proximate said pet door and to control said RFID reader responsive to said identification such that when said pet is proximate said RFID reader is in said operational mode and such that said RFID reader is otherwise in said reduced power mode; characterised in that said pet door comprises a tunnel through which said pet must pass to pass through the pet door; wherein said RFID reader comprises a loop antenna formed around said tunnel; wherein said pet proximity detector comprises a light emitter and a light detector; and wherein said light detector is configured to respond to light from said light emitter reflected by said tunnel into said light detector; whereby proximity of said pet is detected by a detection of a reduction in a level of said reflected light, wherein said light emitter and said light detector are positioned within an angle of 45° to one another, at the top of said tunnel looking down, wherein said light detector is shielded from direct sunlight when said pet door is mounted in a door or wall. an RFID reader to read an RFID tag on a pet; and a lock coupled to said RFID reader to control access through said pet door in response to an RFID signal from said tag; wherein said RFID reader has two modes, a first operational mode and a second, reduced power mode, and wherein said pet door further comprises: a pet proximity detector coupled to said RFID reader to detect when a pet is proximate said pet door and to control said RFID reader responsive to said identification such that when said pet is proximate said RFID reader is in said operational mode and such that said RFID reader is otherwise in said reduced power mode; characterised in that said pet door comprises a tunnel through which said pet must pass to pass through the pet door; wherein said RFID reader comprises a loop antenna formed around said tunnel; wherein said pet proximity detector comprises a light emitter and a light detector; and wherein said light detector is configured to respond to light from said light emitter reflected by said tunnel into said light detector; whereby proximity of said pet is detected by a detection of a reduction in a level of said reflected light, wherein said light emitter and said light detector are positioned within an angle of 45° to one another, at the top of said tunnel looking down, wherein said light detector is shielded from direct sunlight when said pet door is mounted in a door or wall. a pet proximity detector coupled to said RFID reader to detect when a pet is proximate said pet door and to control said RFID reader responsive to said identification such that when said pet is proximate said RFID reader is in said operational mode and such that said RFID reader is otherwise in said reduced power mode; characterised in that said pet door comprises a tunnel through which said pet must pass to pass through the pet door; wherein said RFID reader comprises a loop antenna formed around said tunnel; wherein said pet proximity detector comprises a light emitter and a light detector; and wherein said light detector is configured to respond to light from said light emitter reflected by said tunnel into said light detector; whereby proximity of said pet is detected by a detection of a reduction in a level of said reflected light, wherein said light emitter and said light detector are positioned within an angle of 45° to one another, at the top of said tunnel looking down, wherein said light detector is shielded from direct sunlight when said pet door is mounted in a door or wall.