
My friends and I are out for the night. As the umpteenth round arrives, I finish the last of my water and tap an icon on the screen of my iPhone to log the pint that replaces it. A glowing red number 13 stares back at me. It's the number of units I've drunk tonight – half my weekly allowance.
I tap again and the phone tells me that's 1,278 calories, or the same amount I would have eaten with a rather disgusting fast-food meal inside me.
Ominously, it also says it will take me 2.2 hours of running to burn the booze off.
Welcome to the iDrinkulator, an iPhone application that, providing you're honest, tots up how much you've drunk during the week and what harm it could do.
The thought of a mini nanny state in your pocket may be too much for some but it's awoken my competitive, ahem, spirit and I resolve to get through the week without adding to the total.
iDrinkulator is just one of the hundreds of iPhone apps available from the iTunes store that are now devoted to health and fitness.
Headed abroad and afraid of the mozzies? Download iRepeller, which emits an ultrasound from the phone to scare them off.
Want to get all buff? The originally named 100 Press Ups promises to get you to do just that in six weeks.
Slightly stupid and can't count? Eight Glasses A Day will keep a tally of… how many glasses of water you've drunk.
Some of the apps may seem plain daft but a growing number make full use of the iPhone's inbuilt technology, such as its accelerometer and GPS, to produce applications that will track you when running, walking or biking, calculate your pace or cadence (the speed your pedals turn) and the distance you've travelled before plotting a Google map that will show you just where you've run.
Keen runners and cyclists will be aware of GPS-enabled watches such as those produced by Garmin (www.garmin.com) that cost a small fortune (£200 upwards) but how do they match up to iPhone apps that cost just a few pounds?
We tried two of the most popular GPS apps against the crème de le crème of running watches, the Garmin 405.