Tulsi mala

image released into the public domain by author Madhavi Madhurakavi. Tulsi Mala.

Japa is the Hindu word for repetition of the Lord's name and mala means a chain.There are different kinds of japmalas (Rosary or prayer beads )which are used for different Gods and mantras.A Vishnu devotee generally uses a mala where the beads are carved out from the stem of the Thulsi aka Holy basil plant.
Wearing a Tulsi mala is supposed to be extremely beneficial for the mind,body and soul.It makes a person healthier in body ,calmer in mind and sinless in spirit.
The malas used for wearing are generally much smaller and smoother in finish.There are many varied opinions about the code of conduct to be maintained by a person while wearing them.Interested seekers may adhere to what they believe in.
For another tip to reduce the effects of cell phone radiations with tulsi beads you may refer:

http://simpleayurvedichealthtips.blogspot.in/2010/10/some-ways-to-protect-ourselves-from.html