Repeat notifications for users on-call? For people who are on-call and use android phones.  What's the best way to repeat notifications until acknowledged?  

If an alert comes through at 4AM I may not hear one beep.  But it would be nice if the phone just kept beeping until I acknowledged it.  Is there a way to do this without an extra app?
There is no way to do that with default android and you will need to find applications in order to do that. For example in regards to text messages you can use an application such as GO SMS which has the option to set up a reminder that will set off a different ringtone/alert until you acknowledge the message.

I am sure there are different apps out there that will do this for other notifications such as email if you need it but it might take some work to find the apps you need.