(checked 2026-10-10)Small sample (about 285 ratings); the listing pools sizes and colors.
A Wirecutter top pick and PCMag's 'most durable' tracker: slim, stainless steel and nearly as fast as Tractive, with long battery life thanks to its charging base. But it only fits Fi-compatible collars, goes offline more often than Tractive in Wirecutter's tests, and works best with the app running in the background.
Subscription: Required Fi membership in 6-month, 1-year or 2-year terms (Wirecutter); Fi says every membership includes the Series 3+ collar
Top complaints
- Needs its own collar, which can rattle
It attaches only to collars with Fi's proprietary endlinks. Wirecutter says some users, including one long-term tester, complain about the metal endlinks clicking or rattling.
Source: Wirecutter (GPS pet trackers) - Goes offline; zigzag paths
Wirecutter saw the tracker go offline or fail to connect more often than Tractive's, and its live path sometimes zigzagged through buildings. It also works better if the app stays open in the background.
Source: Wirecutter (GPS pet trackers) - Mixed accuracy and battery for owners
Amazon's review summary says accuracy and durability are mixed, and some owners need to charge every 5 to 6 days while others report phenomenal battery life. Some find it too expensive for what it does.
What owners love
- Fast, sharp tracking in a small package
Wirecutter measured a 16-second average connection to Lost Mode, just behind Tractive, with great accuracy. It weighed about 1 ounce on Wirecutter's scale.
Source: Wirecutter (GPS pet trackers) - Tough and waterproof
It's IP68 plus IP66K for high-pressure water (Wirecutter), and PCMag names it the most durable pick. PCMag's Series 3 review notes the stainless steel case.
- Long battery thanks to the base
Its charging base and Bluetooth/Wi-Fi handoff saves power: it tied Tractive at 71% after 18 walks (Wirecutter). Fi claims up to 3 months per charge.
- You want to keep your dog's current collar
- You won't leave the Fi app running in the background
- You live where cell coverage is patchy
- A slim, tough tracker for active or swimming dogs
- Small dogs (Fi's size chart starts at 5 lb)
- Activity and behavior insights
Scores (tap for why)
What experts say
- Wirecutter (NYT): Top pick for dogs that 'packs a lot into a small device', but you can't use it with just any collar.
- PCMag: Most Durable pick (guide updated 2026-09-22). PCMag's Series 3 review (4.0, Editors' Choice) praised the streamlined design, but escape alerts took three to five minutes.