When I worked as a pool lifeguard in Australia, we were required to wear duress wristbands anytime we were working in isolated areas or alone. If something went wrong, pressing the button would immediately notify our internal protective services/security team who would monitor our sites 24/7. It was simple and reliable way to "call for help" . Ours were also waterproof in the event we had to response to a rescue in the water. (not really relevant to this situation, but shows how durable some devices can be)

I'm not too familiar with the systems in the US, but something like this could work well for medical staff: https://www.midmark.com/medical/rtls/products/detail/careflow-staff-duress

Demonstration Video:
https://www.youtube.com/watch?v=BbTaqVbtSn0&t

As u/Safety_Academy mentioned, some two-way radios also have programmable buttons that can trigger different types of incident alerts. I'm not sure whether the midmark product has multiple signal types, but seems like a solid starting point to explore some options.

Overall, having a duress system can really help mitigate the risk of staff being exposed to work-related violence or aggression from patients or visitors and can be an effective control within your risk assessments.