Why do we ring the bell in a temple?

Is it to wake up the Lord?But the Lord never sleeps.Is it to let the Lord know we have come?He does not need to be told,as He is all knowing.Is it a form of seeking permission to enter His precinct?It is a homecoming and therefore entry needs no permission.The Lord welcomes us at all times.Then why do we ring the bell?
The ringing of the bell produces what s regarded as an auspicious sound.It produces the sound OM,the universal name of Lord.There should be auspiciousness within and without ,to gain the vision of the Lord who is all-auspiciousness.
Even while doing the ritualistic aarati,we ring the bell.It is sometimes accompanied by the auspicious sounds of the conch and other musical intruments.An added significance of ringing the bell,conch and other instruments in that they help frowned any inauspicious or irrelevant noises and comments that might disturb or  distract the worshippers in their devotional ardour ,concentration and inner peace.

As we start the daily ritualistic worsho(pooja) we ring the bell,chanting:
   
Aagamaarthamtu devaanaam
gamanaarthamtu rakshasaam
Kurve ghantaaravam tatra
devataahvaahna lakshanam
I ring this bell indicating
the invocation of divinity,
So that virtuous and noble forces
enter( my home and heart );
and the demonic and evil forces
from within and without,depart