The Nordic Semiconductor nRF52832 present in some Kontakt beacons comes with three RTC.  This enables RTC power saving feature in beacons like Tag S18-3 and BP16-3.

Sources:

https://support.kontakt.io/hc/en-gb/articles/360000291084-Bluetooth-Tag-S18-3-FAQ 

https://infocenter.nordicsemi.com/topic/struct_nrf52/struct/nrf52832_ps.html