OK, so you want an audible alarm
too. My Volvo
2003 instrument panel has an alarm
built into it for low oil pressure or high water
What you can do to add one is buy an alarm - VDO makes one that when it goes off wakes the dead - or find something at NAPA, Autozone, etc.
All you would do is wire it in-line with the wire running from the oil pressure sending unit to the "idiot" light on your instrument panel. When you turn the key on before starting the engine, the alarm will sound until you start the engine and the oil pressure builds and exceeds the "low oil pressure" setting/value of the sender unit. Usually this is around 7 to 10 psi.
You can do the same for your engine high temperature alarm. Again, when the temperature gets too hot and exceeds the setting of the sender unit, the alarm will go off.
Actually having an alarm for engine high temperature is more important than one for oil pressure - you will have a lot more water
pump impellor failures than oil pump failures!
And since you are wiring
things up to the alarm, you can also hook up your bilge
float switch to the alarm and it will sound when the water gets too high in the bilge
You may want to install an off/on switch to the alarm because once it goes off and signals you of the problem, you don't need it to keep sounding while you fix the problem - they are incredibly loud!