Put a quick test circuit together on a breadboard.

Had some MSP430G2211 in the parts bin so used one of those. Using code composer studio and LaunchPad to program / debug. Used Grace to easily configure the pins, P1.6 has internal pull up resistor and the hall effect output. Pin P1.1 has a 2N3904 NPN with the beeper as a low side switch. Basic code for testing everything and the initial video:

int main(void)
{
    Grace_init();                   // Activate Grace-generated configuration
    
    while(1)
    {
    	if (P1IN & BIT6)  //Pin 1.6 is low whenever magnet is detected
    	{
    		//Pin 1.6 is high, turn off beeper
    		P1OUT &= ~(BIT1);  //Clear output bit
    	}
    	else
    	{
    		//Pin 1.6 is low, turn on beeper
    		P1OUT |= BIT1;  //Set output bit

    	}

    }
    
}