if they're in vehicles you can install GPS transmitters in those vehicles. there's not much you can do if your employees are on foot. if these workers disappear you can always dock their pay or fire them.
With their knowledge is easy. They wear a 2-way radio or cell phone with an attached GPS. There are several protocols in use such as APRS. Such systems are in common use by public safety and utilities:
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Lots more...
Without their knowledge is tricky. There are methods that require wearing something. I don't want to go into details unless you really need this.
Without their cooperation is also possible. See:
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Just lock one on the persons neck and follow them anywhere.
Any crop circles or evidence of alien abductions? Such activities are known to cause people to temporarily disappear.
Perhaps surveillance cameras? See how prisons operate for details.
A cheap system would be uhf cb radios that have limited range. Just give them a checkup call every so often and if they dont respond, you know they have gone out of the range. Install repeaters to manage the range boundary.
Seems like you're missing the obvious point, it's useless if they're not carrying it. And human nature indicates people hate being tracked. It's a bordering a bit on the side of 'big brother' to expect people to carry something that does nothing other than let the boss track their activities. At least if you made them carry two-way radios they'd at least hear a voice asking them things. Instead of just a computer gadget that treats them like prisoners.
Then ask yourself how much maintenance you want to put up with. All those gadgets require batteries. You'll have to setup a whole other process for dealing with keeping the units charged. In a farm environment you'd probably need something pretty durable and waterproof, further complicating the charging process, not to mention making them expensive.
Like any other job, you're trading their time for your money. If they get the work you need done in the time alloted, for the money being paid, who cares where they are? And if they're not getting the work done, in the time alloted, then you don't need a gadget to tell you where they went. You fire them for not doing the work required, in the time alloted, for the money paid. Anything else borders on being some sort of fascist dictator. It's bad enough being the boss and having to put up with employees, don't make it worse.
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