I read about these over on Tell Me Something I Don't Know.
From the I Want One Of Those website:
- A transmitter hidden in a cuddly toy wrist-band for your child and there's a receiver alarm small enough to fit on your keyring for you.
- As soon as your child wanders out of the set proximity (between 1 and 20 metres) the alarm sounds, allowing you to take immediate action.
- Switch the alarm to 'Locate' mode and the alarm will sound as soon as you get close to the child.
- The transmitter is available in a cuddly, soft tiger or pink rabbit wrist-band.