Do your vocal warmups with your own piano accompaniment.
• Pick an exercise. (Suggestions for each exercise are included, but you can obviously use them any way you or your vocal coach see fit.)
• Pick a starting note from the keyboard or the musical staff in treble or bass clef. (The range of the exercise will be displayed in blue).
• Select whether you want to transpose up or down a step when the exercise repeats.
• Press Play.
• Adjust the tempo to fit your needs.
• Adjust the time (beats) between repetitions.

•• You can change anything you want while it plays. ••

Don't let your intonation wander by trying to warm up a cappella. Have an accompanist in your pocket.