Afaik steam deck doesn’t have a gps module. You’ve to get any of their identifying information.

What you can do is perhaps sending memes with different cannery token redirects for each worker. Send them around when the device is being used. That way you can compare the grabbed ip with steam log and see which worker’s match. As the deck doesn’t have sim they either will use home wifi or mobile hotspot. Both will work this way.

I’ve a suggestion that might work depending on how honest the perspn hiring the worker is and on their contract. You can tell the person to send some questionnaire or feedback form etc to all of them which will track their ip and name/email (say unique form per worker). Then you can match the ip, as home ips are mostly static for short duration. Tell them to send the form at night or sometime when they’ll be at home and give it a short deadline.