To clear up some possible misconceptions about these products, those on offer include a handful of hardware keyloggers and one GPS tracker.

The keyloggers are devices disguised as regular computer plugs and adapters, and they have to be inserted between the keyboard and the computer. They do not work on laptops or any device with a built-in keyboard. They cannot be seen by the computer software, but they can be seen physically. Hence unless someone has the back of their desktop computer concealed from view and is not ever going to want to get to it, there is a chance that they will see the device and remove it. And there goes your keylogger and the money you spent on it, because if I ever found one on my PC it would be flushed down the toilet for sure.

This may not be an issue for you, but you do need to remember that these are vulnerable to being spotted and identified, if the victim is smart or wise or suspicious enough.

It is generally illegal to monitor a legal adult and if your victim catches you, he or she may report you to the police.

To get the data back out of the device, you need to remove it and install it on a different computer. Afterwards, you need to replace it in the first computer again. This may increase the possibility of your scheme being discovered,

The GPS tracking device is similar in a couple of respects. It stores data which can only be accessed later on, by your retrieving it from the vehicle, loading it into another computer and downloading the data. It then has to be charged and replaced. It is much larger than a USB stick and again, there is a chance of discovery, or simply having it lost somewhere on the road. It is useless as a device to track a stolen car, since you cannot get the data until you recover it anyway.

Be aware that interfering with the privacy of adults is likely to be illegal wherever you are and you always will run the risk of being discovered, more so than if you use software designed to hide itself on a machine. That may have its own limitations, but I would certainly look at both options and especially since software is so much less expensive.

Obviously, if you so badly need to monitor a partner then you have problems you aren't going to solve by buying one of these anyway, but you knew that already.