Flash Bang Grenade

The  is a weapon in Fallout 3 which causes its victims to be stunned.

It is encountered during the escape from Vault 87. The Enclave deploys it against the Lone Wanderer, knocking him/her out in order to transport our hero to the Raven Rock prison facility. There is no way to avoid capture by the Enclave once the grenade has gone off, as it triggers a scripted event.

You can get close enough to see what the grenade is, but you cannot pick it up. The only option you have is "Activate".

Appearances
Although this weapon might be included in future add-ons, it is not available in Fallout 3 yet as it is a scripted item and not a proper weapon in game terms.