The Si720x series of parts where the magnetic field is periodically measured and compared to a threshold. The output pin will go high or low as the threshold is passed.
Typically these 3 pin parts and exceptionally easy to use. Power, ground and the output pin. 5 pin parts have the option of tamper indication on a separate pin and host controlled sampling rate/sleep mode.
More sensitive parts allow a smaller magnet but could be activated by strong background fields.
There is a tradeoff between power and sampling rate. The lowest power parts consume 0.4uA typical but only sample at 5Hz typical.
Some parts offer a “tamper” feature indicating the presence of a stronger than normal magnetic field.
The Si7210 series of I2C parts allows user control of the decision threshold and also allows reading of the magnetic field data. The parts can be put in sleep timer mode for a very low power interrupt (0.4uA Idd average at 200Hz sample rate) when the field threshold is passed. The parts can also be put in complete sleep mode with 100nA typical Idd.
The Si721x series of linear output devices. These devices sample the magnetic field periodically and output the data in analog, PWM or SENT format. Generally they are higher power devices with higher sampling rate. 5 pin parts have the option of a host controlled sleep mode and activation of a built in self-test feature.
These devices can be configured to output the data with either 20mT or 200mT full scale. The more 20mT scale has lower offset and lower noise in mT. The 200mT scale has lower offset and lower noise as a percentage of full scale.
Many of the above choices can be ordered in high Voltage (Vdd= 3.3 to 26.5V) or low voltage (Vdd=1.71V to 5.5V) options.