Have you tried the example in the pull request #2309?
automation:
alias: Garage Door is Open
trigger:
platform: state
entity_id: sensor.garage_door
state: 'open'
action:
service: notify.pushover
data:
title: Garage Door
message: The garage door is open.
target: iPhone,MacBookPro
data:
url: https://home-assistant.io/
url_title: Home Assistant
priority: 1
timestamp: 1466024112
sound: siren
The recent updates for all pushover parameters now support emergency messages that must be acknowledged by the user using the syntax shown below. Pushover does not recommend setting sound in the message but letting the receiver set that in the client “As sounds may change in the future” causing the message to fail. Setting timestamp: true is setting the timestamp to now.
Sounds sent in the message still work for now though correct? I am using group messaging so using different sounds to identify non-critical events are a lot easier than customizing each client (I will use something different for critical messages in the future).