In August 2017 I read a thread in this forum entitled "Keychain GPS Trackers" (https://www.rocketryforum.com/threads/keychain-gps-trackers.141846/) that started me on a seemingly never-ended quest for a cheap (under $35), reliable cellular GPS tracker that would work with a free FreedomPop sim card. I've had some success but am still looking for a better solution. Thought I'd recap my experiences in case anyone else would like to try something similar. Important note: these trackers only work if you have cellular service available at your launch site. I've been to every site in Florida and all have good service. In post #9 of the August 2017 thread, Dugway recommended the MD-601 tracker, which has proven to be my favorite so far, I've bought 3 of them. It is cheap ($26), small, light (22g), and has never failed me, even when more expensive trackers have. You put an app on your cell phone that allows you to track your rocket. Dugway had an issue because his "phone kept shutting down in the 100 degree heat at HellFire when the GPS was active", but I've never had any such issue, even in the Florida summer. The only problem with the MD-601 is that it only works on 2G cellular networks, which in the USA means T-Mobile and its MVNOs. It works fine with the Speed Talk $5 a month sim card, but it does not work with the free FreedomPop sim. Even cheaper (under $20), smaller, and lighter than the MD-601 is the K8 GPS tracker but caution is required when buying, because some versions of this device only track via LBS rather than GPS. It works the same as the MD-601. It also works only on 2G networks and does not work with FreedomPop. See https://www.gearbest.com/car-gps-tracker/pp_643009.html. Another popular tracker is the TK102, which is larger than the MD-601, although cheaper ($11). See https://www.aliexpress.com/item/Rea...and-with-One-Battery-Vehicle/32718561171.html. I don't like it as much because it has no app, it just sends the GPS location and a Google Maps url via SMS text message. Again, it is 2G only. One eBay seller is selling something called the TK102D which he claims works with 3G and 4G sims, but it does not, at least not with AT&T, I bought one but returned it. If you use this or any other type of SMS-based tracker, just before liftoff you should command it to send a text every few seconds, so you'll have an approximate position even if the tracker gets disabled due to a hard or water landing. In August 2017, AT&T had recently discontinued its 2G service, and I wrongly assumed that soon there would be several trackers that would work with 3G and 4G sims like the FreedomPop. I'm still waiting, where are the 3G trackers??? I run Google searches every few weeks and still have not found any. There are many trackers advertised as "3G" but read the fine print and look at the frequencies, they are 2G only. This has to change at some point, but when? I've seen some rocketeers use the proprietary GPS trackers such as Paby, Tracktive, MindMe, and several others that come with a built-in sim card and require a monthly fee. Some have had success with these, and they probably work fine, but the ones I have seen are substantially more expensive and the monthly fees are a lot more than the $5 Speed Talk. I finally found an under $35 solution that works with the free FreedomPop sim, at least for larger rockets. All you need is a used Android phone with Jason Cook's free Insane Rocketry app. This is even better than the above trackers because you get flight data in addition to GPS tracking. And if the phone has a barometer, the app even works as an altimeter and lets you know how high the rocket went. And if you can place the phone into the rocket in a position to take in-flight video, you can use the app to turn the video recorder on and off. Of course, the disadvantage is that phones are larger and heavier than a tracker (135g vs. 20g), but this is not an issue if the rocket has a diameter of 3" or more (a phone in a hollowed out pool noodle is a perfect fit into the payload tube of a 3" rocket). If you don't have an old Android phone lying around the house, for $30 or so you can pick up a Google Nexus 4 or a Motorola Droid Mini on eBay, these and others have a barometer and work well with Jason's app. Also, if for any reason you do not want to use Jason's app, you can locate the rocket by going to https://android.com/find. The best I've been able to find so far for a small device that works with the free FreedomPop sim is the Posh Micro S240, which is a fully functional Android phone with a 2.4" screen. It weighs just 50g and is almost as small as a tracker. The screen cracked as the result of a hard landing but it is still fully functional. The Posh used to be sold brand new for $50 shipped but it is no longer in production. I'd buy another one or two if I could find them for a decent price. There are other phones just as small as the Posh such as the Melrose S9 Plus and the Unihertz Jelly Pro, but I have not tried any of them. I also use a Telemetrum and a Missile Works T3, which have their own transmitters and do not require cellular service. They also work great, but they cost a lot more. That's been my experience, any thoughts? If anyone has seen any other interesting GPS products, please advise.