There are a number of different solutions, depending upon your flying site.
A GPS / GSM tracker uses GPS to find its own location, then a cell phone network to send a text or data stream to the tracking device. These are fine where you have good cell phone coverage and can get Pay as You Go type sims, where you just pay a minimal top up fee to use. This is what I have, as all my flying sites have good coverage and the sim card is only £8 per month. Mine will zero in on an area of less than 2M square. It cost £15 to buy and weighs 45g. An app\on my smart phone shows the location on Google maps and allows me to control the tracker. I can even listen to it's on board microphone!
Radio Locator "Pingers" are used by Birds of Prey owners to track their birds. They use directional receiving antennae with a special receiver to find the pinger. It takes practice to use the kit and it is quite expensive - about £500 for a good system and £200 for even an entry level system. The good points are that they do not require GPS or GSM coverage and the transmitters are very light and small - 5g of so. Range is in excess of 10Km on the high end equipment.
Bluetooth trackers like Tile require close proximity to a mobile device, so are only of use in high density areas, with good cell coverage and plenty of smart phone users. Not really suitable for quadcopters!
Avoid basic pet finders and radio pingers, as they really do not work well. another option would be an audible sounder which can be heard over a few hundred yards, enabling you do find the quad, even if hidden in dense undergrowth.