Remembrance of the Half-Shekel
All men aged 20 and above were obligated to donate a fixed amount to the Temple — half a shekel per person — for communal offerings. Nowadays, in remembrance of those donations, we give tzedakah before reading the Megillah (usually during Mincha on the Fast of Esther). In memory of those coins, it is customary to give the half-shekel with three coins (in those times there were three types of coins, each called "half" — machatzit), and since the word "donation" appears three times in the Torah, we also give three "memorial" coins worth enough to buy 10 grams of silver (as that was the weight of half a Temple shekel).
According to halachic custom, the donation should be given for men over 20 years old. According to other opinions, it should be given for men over 13 years old. Some also give for women. According to the great Rabbi Moshe Feinstein, donations are also given for unborn children (meaning a pregnant woman pays double).
Gifts to the Poor via Bank Transfers
The money must reach the poor on Purim day. In accordance with this condition, and provided the money arrives in the account before Purim day ends, it is permitted to donate money via check or bank transfer (Piskei Teshuvot 694:5).
We transfer the money to those in need in accordance with halacha — on the day of Purim.
