A tuning fork
Vibratory sensation is often assessed using a 128-Hz tuning fork as seen in fig. 1 and fig. 2. Step 1: Strike the tuning fork with your palms so that it vibrates and demonstrate on an upper extremity joint so that the patient knows what the vibration feels like. Step 2: Instruct patients to close their eyes, respond yes when they feel vibration, and let you know when the vibration stops. Step 3: Strike the tuning fork and place it on the 1st metatarsal phalangeal joint. Step 4: Repeat for the opposite foot. Step 5: Compare the time of each foot. If there is a discrepancy in time or if the patient cannot feel the vibration, repeat steps 1-5 on a more proximal joint.
Takahara, Mitsuyoshi, et al. “Assessment of vibratory sensation with a tuning fork at different sites in J apanese patients with diabetes mellitus.” Journal of Diabetes Investigation 5.1 (2014): 90-93.