Wearable that vibrates on text/sms

I am looking for a way to make a wearable (bracelet or hanger) that will vibrate when I send a signal (i.e. text message?). It's intended use is to alert players to certain pre arranged situations in a game. As coach I can not always reach my players across the field by voice so I want to send an alert signal. Also this is more discreet.

A smart watch is to big and volnurable. Bluetooth does not have the range so I am thinking gsm.

Any suggestions on how to build such a device?