I would like to fit my Ikelite housing with the "housing sentry", but the complete kit, which includes flashing red and green lights to indicate whether the vacuum is being maintained, costs $699. Alternatively, I could just buy the vacuum fitting and cap for about $200, and use a syringe and stopcock to withdraw air from the housing.
To give me visual verification that the vacuum is being maintained I could place a small capped syringe inside the housing. As air is withdrawn, the plunger should rise and remain elevated as long as the vacuum is maintained. That wouldn't be quite as good as the complete kit, but it would save me $500.
Does anybody have a better idea for a low budget vacuum indicator? Do you think going the cheap route would leave me open to a disaster that could cost way more than $500?