Question about apps that "prevent phone from going to sleep"

[RobertS975]

I am looking at an app called Voicemail Notifier to give me repeat aural notifications about a VM when I miss the initial signal. The info on it says that it prevents the phone from going to sleep. Does this mean that the battery longevity will suffer significantly?

What does going to sleep actually mean? My screen blacks out after a minute of use, but obviously the phone is still on as I can receive calls, SMS and VMs.

Sorry if this is a really basic question, but I am in the first couple of weeks of my first smartphone, a HTC Inc2 with Verizon.

 

[drdoom]

It means the application is able to keep the screen on if you have it running. If you are done with the app, hitting the homebutton or pressing the power button yourself will override this permission.

 

[amlothi]

It's not the screen. It's whether the phone is running at a fully "active" state, or in a "reduced" state where the processor is slowed down and it will use less power. Usually, if you aren't using the phone and the screen is off, the phone will go into this "sleep" mode. However, some apps keep the phone from sleeping (the screen will still be off, so you won't notice).

If you get the SpareParts app, you can see details about battery usage for apps - in particular, the "partial wake" usage of the battery. This means that the app is preventing your phone from "sleeping" completely and using more battery because of it.