This device appears to be any one of the various magical amulets, stones, etc. 

It gives off a faint dweomer, of course, and if it is held for 1 round by any character an inscription will appear on its surface letting the holder know it is a protective device. 

The possessor gains +1 on all saving throws versus magic, and if no save is normally possible, he or she gains one of 20, adjusted by any other magical protections which normally give bonuses to saving throw dice rolls. 

Thus, this device allows a save versus magic at base 20 against magic missile attacks, for example, and if the target also has +4 for magical armor and +1 for a ring of protection, any roll of 15 or better would indicate that the missiles did no damage. 

The scarab can additionally absorb up to 12 life energy level draining attacks (2 level drains count as 2 absorbings) or death touches/death rays/fingers of death. However, upon absorbing 12 such attacks the scarab turns to powder—totally destroyed. 

1 in 20 of these scarabs are reversed cursed items, giving the possessor a -2 on his or her dice. 

However, 1 in 5 of these cursed items are actually +2 if the curse is removed by a cleric of 16 or higher level. In this latter case, the scarab will have absorption capability of 24 rather than 12.