Various embodiments of a programmable barrier alarm are described. In one embodiment, a programmable barrier alarm comprises a magnet and a sensor, the sensor comprising a magnet and a sensor, comprising a magnetic field detector for sensing a magnetic field produced by the magnet and for producing an electronic signal based on the magnetic field, a processor, and a memory for storing alarm threshold values and processor-executable instructions that, when executed by the processor, cause the sensor to, in a calibration mode of operation, determine a value of a first electronic signal from the magnetic field detector when the barrier is in the closed position, calculate a first threshold value based on the first electronic signal, and calculate a second threshold value based on the first electronic signal, in a normal mode of operation, compare electronic signals from the magnetic field detector to the first and second threshold values, and generate an alarm signal if any of the electronic signals are less than the first threshold or greater than the second threshold.