No subscription. 11 grams. But it's Bluetooth, not GPS.
The Apple AirTag is the most popular "cat tracker" — but calling it a GPS tracker is misleading. It uses Apple's Find My network, relying on Bluetooth signals from nearby iPhones to relay location. In dense urban areas, this network is remarkably effective. In rural areas with few people, you may never get a location update. For indoor cats that occasionally escape in a city, it's an excellent no-subscription solution. At just 11g for the AirTag alone, it's the lightest option by a wide margin. The CR2032 battery lasts about a year. Just make sure to pair it with a breakaway cat collar mount — the AirTag itself doesn't include one.