The Watch Co. on Instagram: “Seiko - S229-5000 Pulsemeter (Alien Watch) 1980-1989. . As early as 1983, Seiko had come out with their first watch equipped with a new…”
WTS] Seiko Pulsemeter : r/Watchexchange
Seiko s234 pulsemeter for $1,300 for sale from a Private Seller on Chrono24