The overall sensitivity of the switch controls the range of the input magnet required for the sensor. Typically, each switching technology can be configured with operating thresholds (B_OP) that are less than 5mT. The total range required for a specific magnet can be determined using simulation tools like the TI Magnetic Sense Simulator.

Electron tunneling in TMR sensors achieves the highest magnetic sensitivity available by magnetic sensors and can be configured for omnipolar operation similar to Hall-effect sensors. That is, that the switch can operate regardless of which magnetic pole is presented to the sensor. This is often useful during product assembly to reduce effort needed to align the magnet. However, there are functions that call for distinguishing which pole has been presented, and in these cases a unipolar switch can be needed as shown in Figure 2-2.

Figure 2-2 Magnetic Switch Output Modes

Hall-effect sensors offer the same functionality with the benefit of versatility in sensing direction, but offer greater flexibility in magnet positioning than TMR sensors. A particular concern that must be considered when using a TMR sensor is that the input magnetic field must always remain below the upper maximum input magnetic field rating. Since the pinned layer of the device is magnetized with a specific polarity, introduction of a significantly strong magnetic field can cause irreparable damage to the sensor. TMR magnetic over-exposure can manifest in the form of offset or even a change in the overall sensitivity of the device. Hall-effect sensors are not subject to this risk, and therefore can be placed as close to the magnet as desired.

In all cases, the input magnetic field must vary in such a way that the maximum input can always exceed the maximum rated value for B_OP and that the minimum field when the magnet is withdrawn is less than the minimum rated value for B_RP. This helps to eliminate risk that a device with an edge condition functions abnormally. In the case of reed switches, the actual construction of the switch can create zones of operation that result from how the individual reeds channel the magnetic field. This can include the possiblity of inadvertent switching zones that are harder to predict without guidance from the manufacturer.

Another challenge to consider when designing with reed switches is that they can experience debounce, which is the result of an elastic collision where the two reeds separate after coming into contact with each other. The debounce extends the settling time of the signal, and can affect transmission integrity if not handled appropriately. The opening and closing of these mechanical contacts can also cause wear and tear over time leading to an eventual failure in the switching mechanism. The amount of switching cycles that it takes to break a reed switch depends on the construction and the load applied to the switch. For higher loads, this breaking point can be between 100,000 and 1,000,000 switch cycles.

A final mechanical consideration with reed switches is that the switches construction prohibits them from being handled as easily as packaged Hall-effect or TMR sensors. In many cases, the enclosure prohibits surface mount installation using standard assembly procedures with a pick and place machine and solder reflow. Care must be taken to not damage the enclosure during the assembly process.