The ACT Supreme Court this week ordered the three month suspended sentence imposed on Bertha Elizabeth Chatfield, 45, by Magistrate Robert Cook be set aside.

Chatfield was instead ordered to sign an 18-month good behaviour order.

The decision, by Chief Justice Helen Murrell, said a police raid on Chatfield's home located the stun gun, which looked like a smart phone, in a drawer of her bedroom.

Chatfield admitted the device could deliver an electric shock to a person and said she had bought it for $50 for personal protection.

But she could not use the weapon because she did not have a charger for the battery.

Chatfield pleaded guilty in the ACT Magistrates Court and was sentenced to three months jail, to be fully suspended upon signing a one year good behaviour order.

Mr Cook, in sentencing, noted that the woman had bought the weapon knowing it was illegal and that it was inoperable.

The magistrate determined the offence had been medium range of objective seriousness.

But Chatfield's Legal Aid ACT lawyers appealed the decision, arguing the sentence had been manifestly excessive.

Lawyer Richard Davies argued the magistrate had erred in characterising the offence as falling within the medium range of objective seriousness, had failed to indicate the nature of any discount allowed for the plea of guilty, the sentence does not take proper account of Chatfield's limited criminal history, and incorrectly concluded that the only option for punishment was jail.

Chief Justice Murrell, in throwing out the sentence, found the offence should not be considered medium range.

Her reasons included that there was no evidence the device had been operational, that Chatfield had ever used it, no evidence that the device had been capable of capable of stunning or otherwise incapacitating the recipient, no evidence to suggest that the device had been used for illegal activity, and the weapon had not been one of the most serious types of prohibited weapons.

"There is reason to believe that the significance of the subjective circumstances may have been overshadowed by the erroneous view that the offence was one of medium objective seriousness," Chief Justice Murrell wrote.

"The objective and subjective circumstances relating to the offence do not dictate that a sentence of imprisonment is the only appropriate penalty.

"In my view, the relevant sentencing purposes are general deterrence, punishment, accountability, denunciation and rehabilitation, and a good behaviour order is adequate to address those sentencing purposes."