A phone call with an intentionally annoying tone. It rings for an extended time, unlike a single notification sound you'd have for email or sms. At my shops it

A phone call with an intentionally annoying tone. It rings for an extended time, unlike a single notification sound you'd have for email or sms. At my shops it's been common practice to use phone calls to escalate, so this works out for me. If your place doesn't/won't do the same, you may be able to use something like Twilio or a less developer-centric, more consumer-focused gateway to call you programmatically on receipt of an event.