Yes, for any cellular tracker: Fi, Tractive, the PetSafe GPS Tracker, Petcube and PAJ all need a plan after any trial. You can avoid a plan with a radio system (Dogtra PATHFINDER2), which only works within range of you, or a Bluetooth tag such as AirTag, which isn't a GPS tracker.
Why cellular trackers charge monthly
A cellular tracker contains a SIM and sends its position over a mobile network every few minutes, or every few seconds in live mode. The plan pays for that connection and for the app's servers.
PAJ includes a SIM and 3 months of premium service; PetSafe includes a 3-month trial. After that, all cellular trackers need a paid plan.
Trackers that work with no plan
- Dogtra PATHFINDER2: GPS over radio to your phone, up to 9 miles, free app.
- Dogtra PATHFINDER2 MINI: the same idea for dogs from about 25 lb, up to 4 miles.
- Apple AirTag: no plan and a year-plus battery, but no GPS; it relies on passing Apple devices.
The trade-off is reach. A radio system can't find a dog that ran beyond its range, and a Bluetooth tag can't find one in an empty field.
Count the plan into the price
Compare trackers over two or three years: device price plus plan. A cheaper device with a pricier plan can cost more in the end. Our subscription calculator adds it up.
Products mentioned

Tractive DOG 6 GPS & Health Tracker
Three U.S. LTE carriers; separate plan required.

Dogtra PATHFINDER2 GPS Tracking & Training System
Up to 9 miles, 21 dogs, no monthly subscription.

Apple AirTag
No GPS, no plan.