Matrix MPU2 Violin Tuner Pickup

Click to enlarge
The MPU-2 is designed specifically for orchestra and band instruments. For string instruments (violin, viola, and cello), the pickup can be clipped onto the bridge to pick up the sound of the instrument for tuning. For band instruments, the pickup can also be clipped onto the instrument to pick up sound.

This is a more reliable way of tuning these types of instruments because of the clip on mic. "Open Air" tuners are more susceptible to ambient sound affecting their tuning reference, where these get only the sound you want.