Featuring a soft silicone rubber body, Squegg's onboard electronics include pressure sensors that measure how tightly (and how many times) it's being squeezed. The ball utilizes a Bluetooth module to transmit that data to a free iOS/Android app on a paired smartphone, where it's displayed in terms of reps and pounds/kilograms of force.
The app also allows users to track their grip-strength-building process over time, and be guided through workout routines. Should they feel so inclined, they can additionally engage in online challenges with other users.
Squegg itself is water-resistant, weighs 66 grams (2.3 oz), and can reportedly run for around 80 hours on one two-hour charge of its lithium battery.
If you're interested, it's currently the subject of a Kickstarter campaign. A pledge of US$29 will get you one in your choice of two colors, when and if it reaches production. The planned retail price is $39.