If you invade this click's personal space, it reacts by sending a stream of ones and zeros to the target board MCU.
Proximity 2 click carries a tiny 2mm x 2mm MAX44000 IC that integrates a proximity and an ambient light sensor. The chip, smaller than a surface mount resistor, consists of an array of photodiodes that convert light into current, and circuitry that converts the resulting current into a digital value.
The stream of ones and zeros is then transported to the target board MCU through mikroBUS™ I2C lines, but there's also a programmable interrupt pin.
The proximity sensing is done through an integrated LED driver (matched to the onboard infrared LED). The sensing range is about 12 cm.
Check out the Libstock example, featuring a buzzer that increases its rate of beeeping as your palm gets closer to it. A parking sensor for the Buggy perhaps?
Details on the product page.
Also, check out the alternative click board for the same task, the original Proximity click, with the VCNL4010 IC.