Apparently, the scanner needs the hand it's scanning to be warm. Action movies didn't prepare me for this!
Aliens are weird little creatures - their kitchen doesn't feature a microwave or oven at all.
Maybe their experiments involve heating things up.
The labs may hold something that could heat up the hand.
Visit the botany lab - the strange machine near the door is, apparently, a microwave.
Use it to heat up the hand.
With the hand nice and warm, the jail cell can open. We finally have a train key!
Next up - the battery.