What are the technical requirements to Android smartphone or tablet?
A phone or tablet with the following specifications -or higher- is fine:
Operating system: Android 5.1
Screen resolution and size: 480 x 800, 4″
Memory: 1 GB of RAM
GPS sensor: required
Camera: recommended, with autofocus
Screen brightness should be suitable for work under strong sunlight.
What about battery?
Apps are by optimized for low battery use. You can let each new labour-shift carry a new fully charged device (Android smartphones are inexpensive), or provide external battery/ power bank to ensure continuous onsite work.