I think most would agree that an alter call song is a song with Lyrics that talk about coming to Christ, God Saving Someone, Or songs that mention Calvary, the cross or the Blood of Jesus washing away sin etc
Examples of Alter Call/invitation songs
It is well in my soul
A wonderful change has come over me (tremaine Hawkins)
Pass me not o gentle savior
Amazing grace
What a friend we have in Jesus
At Calvary
At the cross
If you look in the index of a hymnal, you will see a category called "invitation to dicipleship" or "The Blood". Almost all those songs can be used for alter call
When we say Devotion songs, I think that most of us think of those old Hand clapping, uptempo songs, like "have you tried Jesus" or "Jesus is on the mainline" etc Those are also considered testimony songs. So unlike alter call songs, which are used to draw people to Christ by talking about how he saves,protects and is a friend when you need him, Devotional songs are used to testify how great God has been and are more celabratory.
Thats just how I see it