I was thinking of a vibration sensor on each bin and then if the vibration isn't detected on a Monday between 5pm and 10pm then a voice alert to say: "The bins have not been put out" on repeat every 5 mins until vibration detected.
Depends on where you store your bins. If they are close enough to a wall and always stored in the same orientation, you could use a contact sensor. I don't think vibration is going to cut it. Maybe somebody just moved it.
I agree that a vibration sensor wouldn't be the best choice; somebody could just dump something in the bin, trip the vibration detector at the right time and forget to put it out. Depending on their normal placement you might be able to arrange a motion sensor that gets exposed when they are moved from their parking place during the right time window.
You might try creating a virtual switch "Bin moved" and create a triggered rule that turns the switch on in response to the motion detector. You need to reset this switch on trash day (with another triggered rule). Then when you expect the bins to have put out, have another time triggered rule generate an alert, with a restriction "Bin moved" set by the virtual switch to prohibit it. Bonus points to the person that comes up with a single rule that does all of this
You can define a schedule in Rule Machine.
If your bins are always out together, and your bins are stored in an enclosed area, you can use a simple "electric eye" to trip a contact sensor by soldering wires to the reed switch (some have the screw terminals built in). Both bins are out, the beam is unbroken and the sensor engages.
However, I do like the pressure mat idea from Adam. Seems more robust and unaffected by the elements (snow excepted).
inside the door/window sensor is a tiny glass tube with contacts, one side has a lump of ferrous material. A magnet will move the ferrous material and make/break the contact.
When you open the Door sensor to attach the external wires, you might find screw terminals to use, if not, solder across the reed switch.
I should say—the snow isn’t really an issue, since the only time it will send a false reading is when the trash is already out I just make sure we clean the mat it’s on before putting the bin back.