BEAST SENSOR

There are few good gym workout tracker device in market BEAST SENSOR is one of them . It specially design for your performance lifting weights ,squating exercise or pull ups . It will help you to adjust correct weight,number of sets and reps according to your capacity to achieve your ultimate workout goals. With bluetooth connectivity you can monitor everything directly in your smart phone. Though it is wearable device but it has a little magnet inside so you can attach it with your dumbbell or barbell without fasten in your body.
specification of Product

Onboard Sensors: Type: Accelerometer (3x), Gyroscope (3x), Compass (3x) Acquisition frequency: 50 Hz
Battery: Type: Li-ion fast charge One-charge lifetime: 8 hours
Compatibility: i OS devices: iPhone 4s or newer, iPad 3 or newer Android devices: Android 4.3 or newer Connectivity: Bluetooth 4.0

Source: https://www.thisisbeast.com/en/product