The best way to Hall Effect is here. Easily see when the magnet is close to this hall effect sensor with the onboard blue LED. The LED is Solid to indicate it's power and will turn off when the magnet is near.
This Hall Effect is designed specifically for FIRST Robotics Competition teams. You will find this sensor being used as a limit switch in our line of DART Linear Actuators DART, 12" Actuator Kit (am-3072a) and DART, 6" Actuator Kit (am-3076a).
The sensor works with either pole of the magnet and reading the sensor is easy. 5 volts means the component is safe to move 0v means the magnet is under it. You can use two for mounting and two for a cable tie to hold the connecting cable in place.
Connect this sensor to your robot controller using a male PWM cable into the sensor. Black is ground, red is 5 volts, and white is signal.