To provide a security device and a security system that can improve a security effect.

If a prowler A opens a door 14 to try to enter a house 12, a first sensor 22 detects it, and the output of the first sensor 22 actuates an alarming means such as a buzzer. When an inhabitant or the like tries to enter the house 12, an antenna 26 reads in identification information written in an RFID tag 40 carried by the inhabitant or the like, and a controller stops the operation of the alarming means such as a buzzer. Even when the first sensor 22 detects opening of the door 14, no alarm is raised.