Fi Mini Review: A 16-Gram GPS Tracker for Cats and Small Dogs

The tracker measures 42 by 30 by 12.5 mm on its own, and Fi lists it at 16 grams against 47 for the Series 3+. For a cat or a toy breed that difference matters more than any feature, because a heavy tracker on a small neck gets pawed at, snagged or refused.

It does not come with a collar. Fi supplies a strap and soft silicone cases, and its help center says they fit collars and harnesses from 0.375 inch wide with the strap and 0.5 inch with a case, up to 1.25 inches, as long as there is at least two inches of strap to wrap around. Fi warns against non-slip collars without a buckle and against stacking two attachments on one collar, which can stretch the strap. It also cannot go on a Fi Series 3 collar band, whose magnetic lock is for the larger tracker only.

For a cat, the collar still has to be a breakaway type, and the Mini's light weight does not change that. The tracker is rated IP68 and Fi says it was tested in salt water.

The Mini reports its position over Verizon's LTE-M network, while the Series 3+ uses AT&T and the Fi Ultra T-Mobile. Your phone can be on any carrier, but the tracker's coverage is Verizon's, so Fi's coverage article asks you to check Verizon's map for your home and anywhere your pet spends time. It also warns that the map shows general coverage and not signal strength.

The everyday tools are Safe Zones, drawn on a map in the app, and an alert when the pet leaves one. Inside a Safe Zone the tracker saves battery. Lost Mode switches to live LTE-M and GPS updates and lets you invite family, friends and nearby Fi members through Search Party. Cats get the same Live Map, Safe Zones and Lost Mode as dogs.

What nobody has published is a measurement. No independent test of the Mini's location accuracy or how quickly an escape alert arrives was found, and the only owner account read for this review comes from a cat that has never left its enclosed garden. That is the main reason this section does not score higher, since escape alerts are what a tracker is bought for. Our Fi Series 3+ review covers the same app on the larger tracker.

The battery claim has grown since launch. When the Mini arrived in August 2025, Notebookcheck reported Fi's figure as up to three weeks between charges. Fi's product page and its current comparison chart now say up to two months. The hardware in the help center specs has not changed, and Fi does not say what changed in firmware, if anything.

The word doing the work is "up to". Fi's help center explains that a tracker inside a Safe Zone conserves battery, and that a Fi Series 3 Base near the Mini connects over Bluetooth to stretch it further. A pet that spends most of the day at home, near your phone or a Base, will get close to the long figure. A dog that spends hours outside the Safe Zone every day, or any pet in Lost Mode, will not. Trail & Kale's indoor cat was on track for three to four weeks, an estimate its owners made from six days of wear on a partly charged tracker.

Charging is by USB-C, with a cable in the box and no adapter. Fi's own FAQ points out that neither the strap nor the soft case leaves the port open, so the tracker comes off the collar each time it charges.

For dogs, the Live tab shows steps, a strain score, sleep and a rank against other Fi dogs, and the Health tab adds rest trends and Fi's AI behavior tracking, which watches for changes in licking, scratching, barking, eating and drinking. Cats get activity, rest and their latest trip outside, but Fi's app guide says behavior tracking is not available on cat profiles. Both can store vet records in the app.

None of the health features has been validated independently for the Mini. Treat the behavior alerts as a prompt to watch your pet, since Fi presents them as early signs and not as a diagnosis.

Fi's help center is blunt about it: a Fi membership is required to enable a Mini. There is no reduced mode that shows the location when your phone is nearby, the way older Fi Series 2 collars worked without a plan. If the membership lapses, the tracker stops being useful.

The billing has also changed since launch. Notebookcheck's report described a one-time activation fee and a membership billed every six months, yearly or every two years. Fi's current help center describes two separate charges, one for the hardware at checkout and one for the membership, which starts when you activate the tracker or automatically seven days after shipping. Adding a Mini to a pet that already has an active Fi membership brings no new membership charge.

What the membership buys is Verizon cellular service, the app, Lost Mode and the health features. Before comparing it with a Tractive plan, read our breakdown of what GPS pet trackers cost over three years, which lays out Fi's and Tractive's plans next to trackers with no fee.