Time mine
From Tardis Wiki, the free Doctor Who reference
Time mines are temporal explosives that can be programmed to explode at some point in the future as well as in the past.
Time mines were stored in Vassarian's Battle TARDIS. Heleyna, a Time Lady revealed to be a spy of the Daleks, used a time mine set to explode in the past as a distraction to allow her past self to escape to the star chamber with Ollistra as her hostage (AUDIO: Eye of Harmony).
