This is the 14731st most frequent German word.
notfalls
"If necessary."
The word 'notfalls' indicates a situation where taking the train is an option only if no other solution works.
Notfalls können wir mit dem Zug fahren.
If necessary, we can take the train.
Here, 'notfalls' allows for the use of the speaker's phone if there is no alternative way to meet the need.
Du kannst notfalls mein Telefon benutzen.
You can use my phone if necessary.
In this case, 'notfalls' suggests that calling for help is a last resort when no other options are feasible.