Luckily, security agencies have already solved this particular problem. Instead of texting "Are you okay, please respond [this way]", there's a very simple cha

Luckily, security agencies have already solved this particular problem. Instead of texting "Are you okay, please respond [this way]", there's a very simple challenge-response mechanism. Agent in the field knows the correct response and a duress response to literally any pre-shared question ("How many eggs do you need to make an omelette?" Correct answer: "I'd rather have waffles", duress answer: "three"). All of the "what if [technical fault, stupidity]" is solved by escalation. Replace a text with a phone call in two minutes. Then call an emergency contact in 5. Then call the police in 10. (Adjust numbers to your locale and situational urgency).