This device is a Digital Thickness Gauge, also commonly referred to as a digital micrometer. [1, 2]
It is a precision measuring tool used to determine the thickness of thin, compressible, or flat materials that are difficult to measure with standard calipers. [1, 2]
Key Specifications
Measurement Range: Typically 0 to 12.7 mm (0 to 0.5 inches).
Resolution/Accuracy: Generally 0.01 mm or 0.0005 inches.
Power Source: Usually operates on a single AG13 or LR44 1.5V button cell battery (one is shown in its packaging within your image