A key switch may prevent unauthorized use of the machine but that does not make the machine safe.
You should have a switch on the main lid and the laser compartment…
Post a picture of your laser power supply showing the connectors and we will tell you where to wire the switches into the system.
Amazing, will do, thank you 
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You got an e-stop. That’s good.
See that small black jumper which connects the P and G pins of the power supply? That’s where you connect your safety switches.
If there is no continuity between the P and G pins, the laser can’t fire.
You can add as many switches in series as you like. E.g. you could add an interlock switch for the lid of the engraving compartment and a flow switch.
Since this is logic-level stuff (5 V and a few mA), you can use any switch you like. E.g. a tiny reed switch would also work as an interlock switch.
Brilliant, I’ll get Dave to look this over with me too - maybe take a few pics before we start cutting wires! Hehe … will these be ok to buy?
Yes, P is (water) protect and G is ground.
You could also use any other ground, but this one is meant for this.
You need some JST (XH?) connector for this. However, you could also use two female Dupont jumper wires and secure them with hot glue.
The hot glue can be easily removed in the future with some 99.9% IPA. It creeps under it via capillary action and the glue comes off in one piece. It works pretty well. 99.9% IPA won’t damage the connector, PCB, cables, etc. It’s also used for removing flux residue from PCBs, for example. It evaporates completely if you wait briefly. It’s very convenient stuff. You can also use it to clean the optics (but not the acrylic window).
Amazing, thank you - we’ve ordered the bits so should get this in next week 
thanks for your help, I’ll post pics when it’s done xx
You can also buy JST “pigtails” — usually 10-15cm long — in bundles from Amazon and AliExpress and so forth. Then you can connect those short wires to wires to the interlocks.
Great thank you - Dave’s going to take the lead on this and fit it in the week! All info has been very much appreciated 
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