It is probably known as a personal safety alarm outside Japan. You may be surprised by a selection of personal safety alarms in large supermarket throughout Japan. It is a gadget, sometimes with cute characters, but it has a style.
My 8 years old daughter has two safety alarms. One is for school which she puts on her school rucksack and the other for outside school whenever or wherever she goes after school. It could be a key holder and a neck holder with a long strap.
Unlike the other countries, children go to the local Japanese primary school by themselves without parents' drop-off . It is because Japan is relatively safe (mind you, it is up to now!) and it is usually a walk distance from home to school in a small community.
(Mind you, they make a huge beep! Please turn down the volume before you play.)
Children tend to play with their personal safety alarms rather than what they actually need to use for emergency. It is just like a tale, 'The Boy Who Cried Wolf'.
Whatever reasons, the personal safety alarm is a little charm for Japanese school children from parents.