The LHC normally collides protons into each other. If two protons travelling in opposite directions pass very close to one another within CMS or ATLAS, however, photons radiated from each proton can collide and produce new particles. Precision spectrometers situated on either side of CMS experiment, and a similar project taking shape at ATLAS, will record such events in order to probe the quartic couplings of electroweak bosons and other signs of new physics. Both projects will be installed and commissioned before the LHC restarts in May this year.