I use an aneroid barometer. Tap it and it’s always been accurate up to 12 hours (tap, needle moves anti-clockwise, getting worse, moves clockwise, getting better).
basically, it’s seaweed but more decorative
EDIT – close your windows overnight then open them. If the curtains blow out, the 6 hour forecast is worse than it is now. If the curtains blow in, weather is improving.
These are both highly localised, so likely to be more accurate in the short term and local vicinity than the national forecast, but way off outside a 5 mile radius