I need to break a safety loop on some event. It is a 5v loop to the IO board with a microswitch. I added a relay in series to also break the loop on my new event. The logic is working now I want to make next prototype. I want to replace the relay with a smaller component or even better, use the arduino logic to break the circuit. Any ideas? There are 4 loops, so I am currently using the SunFounder 4 Channel Relay Shield Module. It's only 8 bucks so maybe this is the best way.
How much current? Assuming it is small, how about a reed relay or a transistor; bipolar or FET.
Hi, @bryanbwork
Welcome to the forum.
You are best to stick with the relay contacts to break the circuit as they will be the most reliable and the loop will be isolated from the Arduino,
You can find small PCB mount relays that can be controlled by a 5V signal.
Google;
5v low power relay
The search will give solid state devices, but there are coil tyupe relays as well.
Tom.. 
Was nice to hear about reed relays. Seems viable. I tried a 58050 transistor with a 1kohm resistor but it did not behave reliably. I will also look into FET vs Bipolar. Just looking for search terms and this was very helpful. Thank you.
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That search is problematic because it keeps assuming the control is 5V and I get all the high power relays. But adding reed relay and PCB mount seemed to get me more in the ballpark. Thanks. Glad for the validation of using a regular relay.
Pay attention in your search for a suitable reed relay. Some have a built in flyback diode to protect the Arduino from the switching off of the coil side while others do not. If the diode is not built in, you'll need to add one to your circuit.
Ahh Yes. I see this is an option on digikey. Good point. Thanks. First glance at digikey and I am finding they are pricey and most are out of stock.
A quick look on ebay:
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