Here's why your iPhone doesn't always show the accept and decline buttons when receiving calls

The question has plagued iPhone owners for years: Why can't I always decline an incoming call?

Often the only obvious option given is "slide to answer" - leaving someone trying to avoid a call no choice but to watch their phone ring until voicemail picks up. Those who have spotted the "decline" button wonder why it isn't always there.

I still can't understand why iPhones sometimes have the option to decline a call and sometimes do not.. pic.twitter.com/Mldk0AomTG

- a. (@SativaDominxnt) February 6, 2016

The answer is deceptively straightforward. If your iPhone screen is locked, the slide-to-answer bar appears. But if your screen is unlocked and open, the decline and answer buttons will show.

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When your phone is locked, here's what an incoming call looks like:

Kim Renfro/Tech Insider

If your screen is unlocked when the call comes in, this is what you'll see:

Kim Renfro/Tech Insider

The elusive decline button really bums some people out:

But there's a trick. You actually can decline an incoming call when your screen is locked - it just takes a couple more clicks.

Pressing the lock button once will stop your iPhone from ringing or vibrating. And the second click will decline the call. Voilà! But be warned: The incoming caller will know that you've chosen to decline their call, since your voicemail will kick in sooner than expected.

Now go forth into the world with your newfound knowledge - shared with millions who learned this the last time we explained it - and never stare at your ringing phone screen again.