Kavachas are pendants which we wear around our necks for protection. Kavacha means 'armor'.
These are silver Narasimha Kavachas which are filled with blessed rice, rose petals, and Tulsi leaves which were offered to Paranitya Narasimha on Narasimha Jayanti. The Narasimha Maha Mantra is also written by hand by Swami Vishwatulsidasananda inside each Kavacha.
The Kavacha protects us from all negativity, both inside and outside.
Outside, in the form of jealousy or negative thoughts from other people. Outside, as in bad karma and the negativity from the nine planets (astrology).
And of course, it protects us from the negativity inside: the kind we create in our own minds.
The Narasimha Kavacha easily gets rid of all the obstacles in our spiritual way and in our material life. But more importantly, the Narasimha Kavacha helps erase the negativity which surrounds our hearts so that we can go further and faster on our path of devotion.