[AC Question]

I don't remember my Alternate Password samsung galaxy s5 sprint phone.How can i open?

[B. Diddy]

Welcome to Android Central! So you forgot your primary password and your alternate password? Maybe you could bring it in to your local Sprint store and ask them to help.

[anon8380037]

You can try to lock the device with Android Device Manager with a new pin/password and it will override your lock.
I discovered this by accident when I forgot my ADM lock for a Samsung S2 I loaned out. @Almeuit concurs in a previous post. He wrote the bible (on ADM).

Android.com/ devicemanager (Google account) - Lock. It should be set up by default on a Samsung, but may have been changed in Security settings. You just need your Google log in and a pc, and your phone on data.