The best replacement for siren is mermaid.

The best alternatives to siren are rated as following:
★★★★★  mermaid
★★★  gunzerker
★★  mechromancer
★★  echidna
★★  commando
★  archangel
★  succubus
★  soldier
★  silent hill
★  hal
★  mermaid difference
★  alraune
★  harpy
  homewrecker
  bowtech heartbreaker
  fatal frame
  commando borderlands 2
  amaterasu
  mythic cassiopeia
  sirens
  hunter borderlands
  horn
  ambulance siren
  siret
  hotshotgg and friends
  life lock

Your alternative for siren is not listed? Suggest!
Speaking about siren, one probably shouldn't forget about strobe.

Other search terms related to siren and their ratings are:
★★★★★ strobe
★★★★ strobe light
★ pa system
★ motion detector
★ flashing light
★ motion sensor
beacon
You have in mind a companion for siren and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of siren in all years. Click on graph for more.
siren
mermaid
gunzerker