# The Watch That Watches You

Here's your nightly math! Just 5 quick minutes of number fun for kids and parents at home. Read a cool fun fact, followed by math riddles at different levels so everyone can jump in. Your kids will love you for it.

# The Watch That Watches You

December 29, 2014

Well, it’s really a wristband more than a watch, but there’s a new piece of jewelry that does things for you when you fall asleep. Two teenagers in the UK have made a bracelet that can sense your heartbeat and can tell if you’ve fallen asleep — and at that moment, it tells your TV to start recording the show you were watching! That way you can watch the rest of it later when you’re awake. How did they do this? When we sleep our hearts beat more slowly, by about 8 percent. That means that in the time your heart beats 100 beats when you’re awake, it beats only 92 beats when you’re asleep. The inventors made the bracelet on a 3D printer: instead of putting ink on paper, this machine squirts out layers of melted plastic that stack up into shapes. What else can we get bracelets to do when we fall asleep – play music for us? Make breakfast? High-tech jewelry could get very exciting.

Wee ones: What shape is that bracelet?

Little kids: If you fall asleep at 7 pm while watching TV, and that’s 1 hour earlier than usual, what’s your normal sleeptime?  Bonus: If you always sleep 10 hours, and your bracelet turns on your waffle iron 1 hour before you will wake up, how long have you slept when it starts the waffle iron?

Big kids: If your heart is beating 81 beats per minute, but drops by 7 beats per minute when you doze off, how many beats per minute does it beat now?  Bonus: If you conk out at 8:42 pm, and after 9 1/2 hours your bracelet starts playing music to wake you up, at what time does it wake you?