A programmable barrier alarm includes a sensor, such as a magnetic field detector, for sensing a magnetic field produced by the magnet and for producing an electronic signal associated with the magnetic field, a processor, and, a memory for storing an alarm threshold value and processor-executable instructions that, when executed by the processor, cause the sensor to, in a calibration mode of operation, calculate the alarm threshold value based on a first magnetic field sensed by the magnetic field detector when the barrier is in the closed position, and in a normal mode of operation, compare the electronic signal from the magnetic field detector to the alarm threshold value, and generate an alarm signal if the electronic signal falls below the alarm threshold value.