I don't think they will find standards, what they will have to do is make sure that the positive and negative results are discernible.
I guess the reason he uses haptics is because the device can be kept in the person and the user would not have to hold the device in his hands to receive information on whether the request for help had been sent. through?
I would like to notice a couple of things: why would someone use this to call a recognized emergency service? I have experience in law enforcement and, it is not always the case, but sometimes the fact that an operator can tell the caller to inform any author that the call is being recorded, the police are en route and they can hear everything that is said, it can be a deterrent. Also, here in the United Kingdom (they should consult local policies if it is not based in the United Kingdom) it is recommended to people, even if they cannot speak, that dial 999 and when the operator answers: key 55, the operator will send the call to the police as an emergency call, with similar actions taken in relation to the above.
Secondly; A cell phone call is usually more reliable than sending data, the security provided by an application could be seriously damaged if it does not achieve the purpose of the application.
If there were another user case to really do this, I would make sure that the answer is as identifiable as a result, that is, many applications that provide notifications use a double haptic buzz.
I suggest you look at a pattern that is:
- Easily identifiable
- It is not easily confused with other notifications, including those of the same application
- Any ongoing notification required to indicate that, perhaps, the application is trying again and then changes to a success or continues to indicate a failure.
I hope this helps.