Review on Mini Digital Electronic Thermometer Hygrometer - 12 Pack for Indoor Monitoring in Humidifiers, Greenhouses, Gardens, Basements by Susan Johnson

No switch, so all 'on' packed. They all came without the little strip of plastic preventing contact with the batteries, so who knows how long the batteries will last. These are very small watch batteries (exact type not given) and each unit requires 2. It will most likely be difficult and/or expensive to replace 24 of these when they start dying. error on this +/- 3%? If so, then they are all "exactly". I think they'll give you good baseball readings for temperature and humidity. If that's good enough for you. At worst they showed a 10% (+/-5%) humidity difference when I first unpacked them and 1 has a cracked screen that doesn't show the temperature correctly. Terrible CC. Unreliable. Probably not worth the money.