Bluetooth Trackers vs. GPS Trackers for Bicycle use

 The first thing to clarify is the difference between these two types of devices.

Bluetooth Trackers

By "Bluetooth Tracker", I refer to devices like Apple's AirTag, and Tile Tracker devices.  These are often referred to as GPS trackers, but they are in fact nothing of the sort.  

A real "GPS Tracker" has electronics in it that enable it to receive signals from GPS satellites and determine the location of the device without needing any ground based communication from bluetooth, WiFi, cellular, etc.  This does require a clear view of the sky, however.  There are other satellite based networks, which are technically different than (or extensions to) GPS, such as Michibiki, but I will group them here as GPS to simplify things slightly.  

A bluetooth tracker on the other hand, has no GPS chip or antenna, and thus has no idea where it is located.  

The next major difference is that GPS trackers will generally either store a log of the location history, or have a way to send it back to the owner.  For theft prevention, real time information is generally desired, and thus the latter option is preferred.  For this data transmission, the cellular phone network is often used, though similar wide area networks such as SigFox may also be used.  

A bluetooth tracker has no wide area data transmission capabilities.  This means that even if it did know its own location, it wouldn't be able to send it back to the owner.  

In fact, the only thing a bluetooth tracker can determine is what other bluetooth devices it is nearby - and bluetooth devices have a short range by design.  

The simplest use case for a bluetooth tracker is that you attach it to your keys.  You lose your keys somewhere in your room, so you bring up the app on your phone and select the "find me" button.  Your phone sends a signal to the tracker, it beeps, and you find it stuck in the sofa cushions.  

In this simple case, the tracker and the phone only need to be able to communicate with each other.  

An extended use case would be when another person with the app installed comes in range of your tag.  Their phone detects it, and sends a message back to the tracker company's servers.  The phone sends a list of devices it sees, and its location.  Since the devices are short range by their nature, they must be near the location of the phone.  This means that even though the trackers have no idea where they are, the phone of the visitor knows they are somewhere nearby their own location.  

Although the app doesn't share this information with the owner of the phone, it does sent it back to the servers, which know which trackers belong to who, and route the information back to the app of the tracker's owner.  

This is why you might be able to find a tracker you left outside.  The tracker is well out of the communication range of your phone, but it can talk to a nearby phone, which can talk to the servers, which can relay the message to your phone "Someone located here saw your tag".  

Then you can go to that general area and try to find the tag yourself by making it beep, etc.  

This system is not bad for building small cheap devices that can in effect report their approximate location.  It does depend on being around people with phones that have the app installed, however.  If the devices is in an area without people, or with people who don't have the app installed, then it will never be located.  

Apple has taken this a step further but integrating the app for AirTags into the OS, which means that all iPhone owners effectively have the tracking app installed and running.  This drastically increases the chances of your AirTag being found when compared to the competitors if the tracking devices is left in a less populated area.  

Imagine the thief lives a bit in the country side and has stashed the bike he stole from you in his garage.  He has three friends visit him.  The chances of one of those friends having an iPhone is much larger than the chances of them having any particular tracker app installed.  

If nobody visits him, or if your bike is simply left in the middle of a field or river bank, then nobody may come near it at all for a long time.  

One major disadvantage of bluetooth trackers is that they aren't designed for theft prevention, and therefore some have anti stalking features which would alert the thief to the presence of the device.  

GPS Trackers

GPS trackers do have GPS location chips, and typically some sort of data connection to send their location back to home base.  

The most widely available GPS tracker in common use in Japan is the AlterLock.  Alterlock can determine its location via GPS and report it back to you using SigFox, which is a low speed, low power network used for things like smart power meters.  

If you subscribe to the AlterLock service, then you can track the location of the device using the app if your bike is stolen while the lock is armed.  

(In the current iteration, the lock can't be armed remotely after it is stolen).  

The AlterLock can be set to sound an alarm to deter theives when they are trying to steal your bike, or can be set to silent if you just want to track the location in stealth.  

Since the tracker uses GPS, it may not be able to pinpoint the location if the bike is housed indoors, but it would be able to let you see the location history leading up to being put indoors.  

Also due to the use of GPS and SigFox, the tracker can determine its location and send that back to you even if there are no phones anywhere near it.  

GPS trackers such as the Alterlock are typically larger and mor eexpensive than bluetooth trackers.  The main disadvantage, however, is that they typically need to be recharged around once per month.  

Which is better?

Bluetooth trackers have the advantage of "Set and forget".  The battery lasts a year, and you don't need to "arm" it.   They don't have a deterrent alarm, and rely on phones being around.

GPS trackers such as the AlterLock work even without relying on phones being around, and can have an alarm feature, but need to be charged more often and require a subscription fee.  

Which is better?  I say get both!  They are complementary devices.  

If your bike is valuable I would get the AlterLock, and if your bike is not so valuable, perhaps an AirTag is all you want to invest in - but if you already have an alterlock, adding an AirTag is an easy thing to do that can protect you if the GPS tracker's battery dies.