Could familiar fictional technology become a doomsday threat?

Which ordinary science-fiction technologies might have doomsday potential?

Phasers or phased lasers offer immense power, and transporter systems also raise concerns about destructive potential.

Phasers and phased lasers might bring far more force to bear than their familiar fictional roles suggest. Transporter systems also raise concerns about destructive potential. A device need not have been introduced as a superweapon to invite those concerns. The transporter example remains unspecified, without a particular planet-destroying mechanism.