LOOK: NFL refs used wrist-mounted horns before whistles

MMQB's Albert Breer: How NFL Could Address Dicey Officiating in the Offseason

What to expect from NFL officiating in 2020 - coronavirus protocols, electronic whistles and inexperience - ESPN

Vintage Mcgregor Referees Sports Wrist Whistle Horn Track N Field Football Tough - Sweden

Reconnecting Roots, Baseball: First Pitch, Season 3, Episode 307

Fans' Reactions to Vikings vs. Colts & Largest Comeback in NFL History

Wilson 11 A1000 PF11 Baseball Infielder's Glove - A30-233

Martin SINGLE/BLACK Football Arm Play Holder - A47-841

NFL referee appeared to hip-check a player just before throwing controversial, game-changing penalty flag - Yahoo Sports

What are the black string-like things football referees wear on their hands for? - Quora

What Is The String On a NFL Refs Hand? (and much more about referee equipment)

Referee Magazine - October 2021 by Referee Magazine - Issuu

What are the black string-like things football referees wear on their hands for? - Quora

PACKAGE--- 2PCS plastic whistles with lanyards. These whistles are great for referees, coaches, training, teachers, survival, emergency, school, gym,

Whistle, 2 Packs Plastic Sports Whistles with Lanyard, Loud Crisp Sound Whistle Ideal for Coaches, Referees, and Officials

What are the black string-like things football referees wear on their hands for? - Quora

PACKAGE--- 2PCS plastic whistles with lanyards. These whistles are great for referees, coaches, training, teachers, survival, emergency, school, gym,

Whistle, 2 Packs Plastic Sports Whistles with Lanyard, Loud Crisp Sound Whistle Ideal for Coaches, Referees, and Officials