BTW, while looking for a solution for a different topic (someone who wants to know when the Roomba is away from the docking station), I decided to check the cost of some high sensitivity pressure mats. These are ones that will trigger with just 5 pounds of pressure instead of the typical 25 pounds.
LondonMat makes a nice variety, including some that trigger at 5 pounds of pressure for around $50. That’s just the mat, you still need to connect to a sensor exactly as with the United Security mat.
The downside is that the LondonMat switching mat will trigger from cats and dogs. But for something like a Roomba docking station, could be nice. So just one more option for a slightly different use case.