Yes, you could use a AirTag or similar, but this is LTE-M enabled with a SIM and full GPS, and it powers down into an idle mode while the pet is at home. It ends up having a 6-month battery life.
The collar is built around a Nordic Semiconductor NRF-9160, a System in a Package (SiP) that does most of the heavy lifting as it includes GPS, an LTE-M modem, and an ARM processor. One interesting feature here: [Sahas] doesn’t make his antennas on the PCB, but instead uses an Ignion NN03-310, an off-the-shelf antenna that is already qualified for LTE-M use. That means this system can be connected to almost any LTE-M network without getting yelled at for using unqualified hardware and making the local cell towers explode.
As one commentator says, it is really well documented and designed, and looks much like a product designed by Apple themselves. So, an iOS app is expected, but there are no plans to produce an Android app, although the dev says he is open to someone from the community creating one.
See https://hackaday.com/2023/09/19/open-source-tracker-keeps-an-eye-on-furry-friends/