She counts calories on her iPhone. She tracks her runs on RunKeeper (or Nike+). She has even inversely correlated her weight against the number of hours she sleeps each night.
If that sounds like someone on your holiday gifting list, you might want to take a look at Fitbit One Activity + Sleep Tracker. The device records the number of steps taken, stairs climbed, distance traveled and calories burned each day. It also measures how many hours you've slept and the number of times your sleep was interrupted during the night. All of that data is synced over Bluetooth to Fitbit's website and companions apps for iOS (and soon, Android) devices. Charts and graphs help you identify patterns in the data and make better choices about healthy living.
"The One" is about the size of a USB stick and can be clipped onto your belt or bra, inserted in a wristband or tucked in your pocket. It's waterproof and its battery lasts five to seven days before needing a recharge. You can also sync the data you record with other apps you're using, including Endomondo, LoseIt, RunKeeper, MapMyFitness, MyFitnessPal and SparkPeople.
Or pick up Fitbit's Wi-Fi Smart Scale for $129.99, and you'll be able to automatically sync your weight with the other data you're recording.
Price: $99.95 (including shipping)