There are more answers to this question that might be however the most interesting one…
A person who finds Tefillin on Shabos – Wears the Tifillin.
Also a person who is coming from Chutz L’tchum into town ,and has his Tefillin still on his head .
Also a person who was in the Bais Hamedrish in the field wearing Tefillin ,
comes back into town , keeps wearing the Tefillin ,puts his hand on them ,until he reaches his home.
SEE Be’ah 15a , and Eruvin 95b