What musical instrument sounds like a backup beeper?

[Cartoondude135]

I'm making something super special: a made from scratch backup beeper sound effect. Just like that backhoe loader pushing the trash into the pit, it sounds like an F-note "beep-beep-beep". But... does anybody by any chance know of any digital version of a musical instrument (via softwares like Studio One) that sound similar to or almost identical to a backup beeper? That's the edge I need to replicate this specific F-note backup beeper sound. (I.E, Foley art.)

 

[happyrat1]

Just set up a square wave, zero attack and minimum sustain and release with a slightly detuned second oscillator also set to square and you should have a pretty decent facsimile.