It depends what type of bleed screw is fitted to your radiator.
For radiators with a slotted bleed screw, a simple screwdriver represents an ideal alternative to a bleed key. Just insert the screwdriver into the slot and turn it in a counter-clockwise direction to bleed the radiator.
If your radiator features a different sort of bleed screw, perhaps including a square or hexagonal orifice within it, there are other alternative options.
You could use an Allen key, spanners or a plier to grip and twist the nut for an effective radiator bleed.
If you want to know more about the basic principles of the process, check out our Advice Centre guide, How to Bleed a Radiator.