Sensor battery life varies for each device, and can depend on how much use the device gets. Here are general guidelines on battery life and replaceability:

E8 Asset Tracker: Replaceable CR2032, up to 1 year battery life

Flic Button: Replaceable CR2032, 2-3 year battery life

HOBO MX-100 Temp Monitor: Non-replaceable, 1 year battery life

RS40 Occupancy and Motion Sensor: Replaceable AAA batteries, up to 5 year battery life