I bought a set of pitch pipes once so that I could practice singing whilst driving my campervan. As a guitarist I knew which key I wanted to sing in so it was all straightforward.

If you don't have any playing skills it will be hard to work out keys for yourself and it seems to me that pitch pipes are not the best tool for the job. A small keyboard at home would help you discover what I call the working range of your voice.

From the highest note you can comfortably sing to the note below which all volume is lost.

Then, song by song, you find the highest and lowest notes. From that you work out which key matches the range of the song to the range of your voice. Note that down and at your next session ask someone to give you the right note to start.

A whistle is small enough to carry in an inside pocket. Find your starting note on that and you won't have to ask someone else for a note.