My Christmas present to myself has been a Timex Ironman digital watch.

I know it sounds sad enough buying a digital watch without it also having a stupid name like "Ironman" (only a man made of Iron would be cool and macho enough to wear a digital watch), but the real reason I have bought it is to assist me in my Marathon training.

Not only does the timepiece include a stopwatch, but it also comes with a little box that you strap round your arm which takes advantage of satellite technology in order to follow your progress and tell you exactly how far you've run (as well as what your average and maximum pace was during your run). You might argue that an A to Z and a piece of string might have been a cheaper alternative. And you'd be correct. But thanks to my watch I know that I ran exactly 7.285 miles yesterday in 1 hour 16 minutes and 32 seconds and that I was running at a disappointing 5.5 miles per hour (though at one point I was doing a more impressive 20.3 miles per hour. If I can keep that up I can comfortably beat the Marathon world record).

I have to say that it is already worth the exorbitant asking price, partly because knowing how far I am running is really going to spur me on to try and go even further and partly because Marathon running lightweight Emma Kennedy is extremely jealous of me. You'll see, she'll be buying one of her own soon enough. Where I go, she shall follow. About two hours behind me, when it comes to the Marathon.

The box that staps on to your arm is about the size of a pack of playing cards and communicates with 12 satellites to pinpoint your exact position and calculate all the other statistics I've mentioned. I am not sure that the bloke who invented satellites realised that his invention would be used to check the progress of a plodding, fat man traversing the back streets of West London. He probably thought it would be used for international espionage, but he was mistaken.

Much as I love this perverse misuse of technology it does have slightly frightening ramifications. Essentially I am voluntarily wearing an electronic tag, which is capable of pinpointing my exact position on the planet as long as I'm not indoors (no more running through M&S for me then). Imagine how the government could use this information if they wanted. "Look a fat man is moving at slightly more speed than we would usually expect along the banks of the Thames near Barnes... let's use that information to...er... compromise his freedom in some way."

I am quite tempted to wear my tag all the time. Then if I am ever implicated in a crime that I didn't commit, I can prove my exact whereabouts (and average speed) beyond any reasonable doubt. Of course a clever lawyer might argue that there was nothing to prove that it had been me wearing the tag. It's removable, emplying velcro for ultimate convenience and I could just have attached the tag to a friend or a stray dog (I could be caught out by a sudden improvement in my agility and average pace if I did that though). So in order for this scheme to work I will have to have the tag grafted onto my arm, perhaps screwed into my arm bones for absolute certainty, with a claw on it that will rip out my heart if I try to remove it.

The downside of this will be that if I ever do commit any kind of crime then the police will pretty much have me bang to rights. Unless I commit the crime indoors. So my Starbucks ginger biscuit heists can still continue unabated.

I think that I am more likely to be falsely accused of a crime than actually commit a crime, so the arm bone skewering and heart-claw arrangement may well go ahead.

But what price the ability to judge the pace of a plodding fat man? If they can do this so easily then imagine what other freedoms are being compromised. If you've got any fillings then I think you should be afraid.

Unless you're indoors.

Where you're safe.

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