How do I know if my oven needs an indicator light?

Most ovens operate with an electronic thermostat. This means that even though the appliance may boast a Sabbath mode, when you open the door and cold air enters the oven, an electronic device is measuring the change in temperature. If the door is opened when the element is not in operation, the change in temperature will accelerate the turning on of the element. Many poskim are concerned about this and pasken that the oven door should not be opened due to this issue.

If, however, the door would be opened while the element is operational, the change in temperature will not affect the appliance.

Therefore, on Shabbos, an oven door should only be opened when the element is operational. If your oven does not have a built-in indicator light, the FedTech indicator light is the solution for Shabbos use of the oven.


How do I arrange to have an indicator light installed?

Please click here to send us your contact details, and one of our team will get back to you to arrange payment and installation.


Once installed, what are the usage instructions?

On Shabbos, the door of the oven should only be opened when the indicator light is brightly lit – this shows that the element is working. Opening the door at this stage is halachically permitted.

Please note that the light will have an almost constant dim glow – the door may not be opened on Shabbos at this time.


Which issues does the indicator light NOT resolve?

The indicator light only resolves the problem related to the indirect interaction with the thermostat when opening the door. There are other issues to remember when using an oven on Shabbos:

  • Does the oven have a door switch which directly controls the light fan digital display screen. These can normally be tested by the user.
  • Does the door switch control the heating element switching it off when the door is opened. This will normally need to be tested by an electrician or FedTech may have information on your model.
  • Food must not be placed in the oven on Shabbos. Instead all food must be fully cooked and heating in the oven as Shabbos commences.


Are there ovens with which the indicator light will not work?

In recent testing, some new ovens have been found to make use of two heating elements in their Shabbos mode.

This means that when using Shabbos mode, they will NOT be compatible with the FedTech indicator light. This is because whereas the door should not be opened until both heating elements are lit, the light will show with one heating element.

In many cases the oven will still be usable without the indicator light and this will NOT be a concern. For example, many NEFF ovens can be used in CircoTherm mode as this mode operates only one heating element. It is important to check that the mode which is to be used does not carry any of the concerns mentioned in the previous question.

Before purchasing any oven, the public are advised to contact FedTech by emailing


How does the device work?

The device will be installed in a non-invasive manner and will take a constant reading of the current flowing through your oven’s power cable.


If my appliance is serviced by the manufacturer’s technicians, how should the device be explained to them?

Neither Laser Know How Ltd nor FedTech take responsibility for your oven’s warranty. If a technician questions the indicator light, we recommend you stress that the device is only attached to the power cable, and is completely non-invasive with regards the operation of the appliance.


Who do I contact if I have trouble with the device?

As a first port of call, please call your technician. If he advises that the device is faulty, please be in contact with FedTech and we will do our best to resolve any issues.


Who has manufactured the device?

Laser Know How Ltd is responsible for the Made Safer Hotplate (see Its mission is to provide bespoke solutions to the challenges facing the shomer Shabbos householder in the 21st century.

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